Production of a Light-gated Proton Channel by ... - ACS Publications

Replacing the Retinal Chromophore with Its. 2. Synthetic Vinylene Derivative. 3. Riho Takayama. †,┴ ..... ms.com/home.html) for the English langua...
0 downloads 3 Views 1MB Size
Subscriber access provided by University | of Minnesota Libraries

Biophysical Chemistry, Biomolecules, and Biomaterials; Surfactants and Membranes

Production of a Light-gated Proton Channel by Replacing the Retinal Chromophore with Its Synthetic Vinylene Derivative Riho Takayama, Akimasa Kaneko, Takashi Okitsu, Satoshi P. Tsunoda, Kazumi Shimono, Misao Mizuno, Keiichi Kojima, Takashi Tsukamoto, Hideki Kandori, Yasuhisa Mizutani, Akimori Wada, and Yuki Sudo J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b00879 • Publication Date (Web): 11 May 2018 Downloaded from http://pubs.acs.org on May 12, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

1

Production of a Light-gated Proton Channel by

2

Replacing the Retinal Chromophore with Its

3

Synthetic Vinylene Derivative

4

Riho Takayama†,┴, Akimasa Kaneko†,┴, Takashi Okitsu‡,┴, Satoshi P. Tsunoda&,%, Kazumi

5

Shimono^, Misao Mizuno#, Keiichi Kojima†,§, Takashi Tsukamoto†,§, Hideki Kandori&,

6

Yasuhisa Mizutani#, Akimori Wada‡ and Yuki Sudo†,§,*

7



Faculty of Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan

8



Laboratory of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe 658-

9

8558, Japan

10

&

11

%

12

0012, Japan

13

^

14

#

15

Japan

Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555, Japan PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-

Faculty of Pharmaceutical Sciences, Toho University, Funabashi 274-8510, Japan Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka 560-0043,

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

16

§

17

Okayama 700-8530, Japan

Page 2 of 21

Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University,

18 19

AUTHOR INFORMATION

20

Corresponding Author

21

*

[email protected]

22 23

ORCID

24

Yuki Sudo: 0000-0001-8155-9356

25 26

AUTHOR CONTRIBUTIONS

27



These authors contributed equally to this work.

28

29

ABSTRACT. Rhodopsin is widely distributed in organisms as a membrane-embedded

30

photoreceptor protein, consisting of the apoprotein opsin and vitamin-A aldehyde retinal, A1-

31

retinal and A2-retinal being the natural chromophores. Modifications of opsin (e.g., by

32

mutations) have provided insights into the molecular mechanism of the light-induced functions

33

of rhodopsins as well as providing tools in chemical biology to control cellular activity by light.

34

Instead of the apoprotein opsin, in this study, we focused on the retinal chromophore and

35

synthesized three vinylene derivatives of A2-retinal. One of them, C(14)-vinylene A2-retinal

ACS Paragon Plus Environment

2

Page 3 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

36

(14V-A2), was successfully incorporated into the opsin of a light-driven proton pump

37

archaerhodopsin-3 (AR3). Electrophysiological experiments revealed that the opsin of AR3

38

(archaeopsin3, AO3) with 14V-A2 functions as a light-gated proton channel. The engineered

39

proton channel showed the characteristic photochemical properties, which are significantly

40

different from AR3. Thus, we successfully produced a proton channel by replacing the

41

chromophore of AR3.

42

TOC GRAPHICS

43

44

KEYWORDS Photoactive protein • Ion transport • Rhodopsin.

ACS Paragon Plus Environment

3

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 21

45

Rhodopsin, a seven-transmembrane photoreceptor protein, is widely distributed in all domains of

46

life, including archaea, bacteria and eukaryotes, indicating its biological significance for

47

organisms.1, 2 Rhodopsin consists of an apoprotein opsin and vitamin-A aldehyde retinal, with

48

A1-retinal and A2-retinal being the natural chromophores (Figure 1A).3 Those retinals bind

49

covalently to a conserved Lys residue on the seventh (or G) helix of opsin via a protonated

50

retinal Schiff base (PRSB) linkage, where the positive charge is stabilized by a negatively

51

charged calboxylate called the counterion (Figure 1B).4 Light absorption by rhodopsins triggers

52

the isomerization of the retinal chromophore within several hundred femtoseconds and the stored

53

energy in the excited state induces a stepwise photoreaction with structural changes of the opsin,

54

that lead to a variety of photobiological functions including photo-energy conversion and photo-

55

signal transduction.

56

utilized as tools for optogenetics, a method to control cellular activity by light in vivo.5 On the

57

basis of that background, to understand and utilize rhodopsins, researchers are extensively trying

58

to modify the protein moiety (i.e., insertion, deletion and/or replacement) and both the

59

production of color variants and functional conversions have been achieved by strategic

60

mutations.6-9 Alternatively, in this study, we focused on the “chromophore” to modify the

61

functional and photochemical properties of rhodopsins.

1, 4

In addition to their biological significance, rhodopsins have been widely

62

Three derivatives of A2-retinal, C(6)-Vinylene A2-retinal (6V-A2), C(10)-Vinylene A2-

63

retinal (10V-A2) and C(14)-Vinylene A2-retinal (14V-A2), each of which possess a long π-

64

conjugation system on the polyene chain (Figure 1A), were newly synthesized by an organic

65

chemistry method with overall yields of 12, 4 and 9%, respectively (Supporting Figures S1-S4).

66

Due to the extension of the π-conjugation system, the absorption maxima of these derivatives

67

(420 nm for 6V-A2, 418 nm for 10V-A2 and 421 nm for 14V-A2) were largely shifted to a

ACS Paragon Plus Environment

4

Page 5 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

68

longer wavelength than that of A2-retinal (376 nm). The spectral red-shifts are explained by a

69

reduction of the energy gap between the electronic ground- and excited- states of the retinal

70

chromophore.10 The opsin of Middle rhodopsin (Middle opsin, MO) was firstly employed as a

71

protein template because MO characteristically accepts a variety of retinal isomers, 9-cis, 11-cis,

72

13-cis and all-trans, which suggests that it has a large cavity around the chromophore.11,

73

According to standard methods and procedures, MO was expressed in Escherichia coli cells with

74

natural retinals (A1 or A2) and the synthesized A2-retinal derivatives (6V-, 10V- or 14V-A2). E.

75

coli cells expressing MO with the three synthesized derivatives showed an orange-red color

76

(Supporting Figure S5A), indicating the successful incorporation of those derivatives into MO.

77

During the purification, the color of MO with 6V-A2 or 10V-A2 changed to yellow due to

78

denaturation, while MO with 14V-A2 was successfully purified with a visible color in the

79

detergent n-dodecyl β-D-maltoside (DDM) and its absorption maximum appeared at 504 nm,

80

comparable to that of MO with A2-retinal (508 nm). Those results suggest the breakage of the π-

81

conjugation system on 14V-A2 in MO. The biological function of MR is still unclear, so we

82

moved on to a second rhodopsin template, archaerhodopsin-3 (AR3).

12

83

AR3 works as a light-driven outward proton pump, which is one of the most typical

84

biological functions of rhodopsins, and is applicable for optogenetics as a neural silencer.13 Cells

85

expressing archaeopsin-3 (AO3) with natural retinals (A1 or A2) or the three retinal derivatives

86

(6V-, 10V- or 14V-A2) showed a slight orange color for AO3 with 6V- or 10V-A2 and a purple

87

color for AO3 with 14V-A2 (Figure 1C), suggesting their successful expression in the cell

88

membrane. As reported,8, 14 light-induced decreases in pH were observed for cells expressing

89

AO3 with A1-retinal or A2-retinal, and treatment with the protonophore carbonyl cyanide 3-

90

chlorophenylhydrazone (CCCP) strongly impaired those pH changes (Figure 2A), indicating

ACS Paragon Plus Environment

5

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 21

91

their light-driven “outward” proton transport activities. On the other hand, for AO3 with 14V-

92

A2, light-induced increases in pH and their inhibition by CCCP were observed, indicating a

93

light-induced “inward” proton movement. Increases in pH were also observed for AO3 with 6V-

94

A2 or 10V-A2 (Figure 2A). These results suggest that the inward proton movement of AO3 with

95

6V-, 10V- or 14V- A2 retinal derivatives is caused by addition of the vinylene (-C=C-C-) group

96

to any position on the polyene chain of the retinal. As occurred with MO, the color of AO3 with

97

6V-A2 or 10V-A2 rapidly changed to yellow during purification, while the purple color of AO3

98

with 14V-A2 was maintained for several days. Therefore, AO3 with 14V-A2 was used for

99

further investigations. As shown in Figure 2B, the absorption maxima of purified AO3 with A1-

100

retinal (i.e., wild-type AR3), A2-retinal or 14V-A2 were located at 556 nm, 584 nm and 543 nm,

101

respectively. The spectral red-shift of A2-retinal (+28 nm) compared with A1-retinal was

102

explained by the extended π-conjugation system on the polyene chain. On the other hand, a large

103

spectral blue-shift was observed for 14V-A2 (-41 nm) compared with A2-retinal. Judging from

104

the color of the cells (as shown in Figure 1C), a spectral blue-shift was also likely to be observed

105

for AO3 with 6V-A2 or 10V-A2. These results suggest that addition of the vinylene group

106

commonly induces breakage of the π-conjugation system on the polyene chain with different

107

magnitudes.

108

The dose-response relationship between light intensities and initial slope amplitudes of

109

the light-induced pH changes showed a linear regression at a low light intensity below 6

110

mW/cm2 (Supporting Figure S6). Therefore, we employed a light intensity of 6 mW/cm2 and

111

obtained action spectra. The absorption spectra of AO3 with A1-retinal, A2-retinal or 14V-A2

112

matched well with their light-induced proton transport activities (Figure 2C), indicating that light

113

absorption of AO3 with 14V-A2 leads to its inward proton transportation. To confirm whether

ACS Paragon Plus Environment

6

Page 7 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

114

the proton movement is by active transport (pump) or by passive transport (channel), we

115

performed electrophysiological experiments (Figures 2D-F). For illumination, we used a xenon

116

light source through a 580 nm band-pass filter. Figure 2D shows a whole cell patch-clamp

117

recording of murine ND7/23 cells expressing AO3 with A1-retinal (i.e., wild-type AR3, left) or

118

AO3 with 14V-A2 (right) at different extracellular pHs (pHo = 7.2 and 4.5) and +20 mV of

119

holding potential. Positive currents upon illumination were observed for AO3 with A1-retinal

120

both at pHo 7.2 and 4.5, whereas positive and negative currents were observed for AO3 with

121

14V-A2 at pHo 7.2 and 4.5, respectively. Similar experiments were then performed under various

122

membrane holding potentials ranging from -100 to 60 mV to obtain the current-voltage

123

relationship (I-V plot) of the photocurrent (Figures 2E and F). Positive currents were observed

124

for AO3 with A1-retinal at all holding potentials (Figure 2E), representing the active proton

125

“pump” activity from the inside to the outside of the cell. In contrast, the direction of the currents

126

for AO3 with 14V-A2 was influenced by the membrane potential and a reversal of the potential

127

appeared around zero at pH0 of 7.2, where the proton gradient (delta pH) between the inside and

128

the outside of the cell is expected to be around zero (Figure 2F), suggesting a passive proton

129

“channel” activity. From these results, we concluded that AO3 with 14V-A2 works as a light-

130

gated proton “channel”. Thus, the addition of a vinylene group into the retinal chromophore

131

converts a proton pump into a proton channel. A transient outward current and a rapid current

132

reduction concomitant with the start and stop of illumination were observed in the current traces

133

of cells expressing AO3 with 14V-A2 (Figure 2D), which suggests that AO3 with 14V-A2 also

134

works as a leaky outward proton pump similar to natural light-gated proton channels.15, 16

135

To characterize the photochemical properties of AO3 with 14V-A2, we performed

136

further spectroscopic analysis (Figure 3). Firstly, we carried out pH titration experiments to

ACS Paragon Plus Environment

7

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 21

137

estimate the pKa of the counterion (Asp95) of the PRSB (Figure 1B). Upon acidification, the

138

absorption maxima were shifted from 556 nm to 573 nm for AO3 with A1-retinal (i.e., wild-type

139

AR3), from 584 nm to 600 nm for AO3 with A2 and from 543 nm to 553 nm for AO3 with 14V-

140

A2 (Figures 3A-C). These large spectral red-shifts were explained by protonation of the

141

counterion, which drops the energy gap between the electronic ground state and the excited

142

state.10 In the difference spectra, the maximal absorption changes were located at 618 nm for

143

AO3 with A1-retinal, at 668 nm for AO3 with A2-retinal and at 641 nm for AO3 with 14V-A2.

144

The absorption changes were then plotted against various pH values and the data were fitted by

145

the Henderson-Hasselbalch equation with a single pKa value of 3.10 ± 0.13 for AO3 with A1-

146

retinal, 3.05 ± 0.03 for AO3 with A2-retinal and 3.39 ± 0.08 for AO3 with 14V-A2 (Figure 3D).

147

The slight upshift of the pKa in AO3 with 14V-A2 suggests that the environment of the PRSB of

148

AO3 with 14V-A2 is slightly different from those of AR3 with A1-retinal or A2-retinal. We then

149

performed resonance Raman spectroscopy to investigate the chromophore structure (Figure 3E).

150

As seen, hydrogen-out-of-plane (HOOP) vibrations appearing at 950-1000 cm-1 were similar

151

between the three retinals (A1-, A2- and 14V-A2). For C-C stretching vibrations appearing at

152

around 1200 cm-1, the vibrational frequencies for AO3 with 14V-A2 were down-shifted from

153

those for AO3 with A-2-retinal (1201 cm-1  1177 cm-1, 1180 cm-1  1159 cm-1 and 1170 cm-1

154

 1149 cm-1) (Figure 3E). It has been reported that torsions around single bonds of the retinal

155

chromophore could be seen as down-shifts of vibrational frequencies in the finger print region,17

156

suggesting the torsion of the conjugated polyene chain around a single bond(s) in the binding

157

pocket of AO3 with 14V-A2 which is expected to give rise to a blue shift of the absorption

158

maximum. For C=C stretching vibrations appearing at 1500-1550 cm-1, when C(3) and C(4) are

159

dehydrogenated (i.e., AO3 with A2 or 14V-A2), a splitting in this mode was observed with the

ACS Paragon Plus Environment

8

Page 9 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

160

new peaks lower than the band around 1530 cm-1 in trans-retinal. This phenomenon has already

161

been reported both for bacteriorhodopsin and for bovine rhodopsin and has been interpreted that

162

it results from a carbon-carbon hydrogen bond contribution involving the hydrogen at C(9) or

163

C(13) and the nearest double bond.18 This contribution makes it possible to alter the two lowest

164

energy C=C stretching modes. These bands have been reported to be generally deuteration

165

insensitive.18 Of note, the amplitudes of the deuteration shift of the C=N stretch band of the

166

retinal appearing around 1640 cm-1 was 11 cm-1 for AO3 with 14V-A2, which was significantly

167

smaller than those for AO3 with A1-retinal and AO3 with A2-retinal (18 cm-1) (Figure 3E). It is

168

known that a smaller deuteration shift of the C=N stretching frequency means a weaker hydrogen

169

bond formation between the PRSB (Lys226) and its counterion (Asp95).19 Thus, these

170

observations indicate that the hydrogen-bond strength of the Schiff base in AO3 with 14V-A2 is

171

weaker than those of AO3 with A1-retinal or A2-retinal. From these results, we concluded that

172

the structure around the Schiff base in AO3 with 14V-A2 is different from those with A1-retinal

173

or with A2-retinal. Because the Schiff base region is altered upon illumination with

174

isomerization of the retinal and plays an important role in the biological function of rhodopsins,

175

the structural difference would be related to the functional conversion from the proton pump into

176

the proton channel.

177

Finally, to investigate the photoreaction kinetics, we carried out flash-photolysis

178

experiments from millisecond to second time frames (Figure 4). The apparatus and procedures

179

were essentially the same as previously reported.20 Upon illumination with light above 520 nm,

180

the three variants commonly showed both a depression of the initial state absorption (540 – 590

181

nm) and the formation of two photointermediates at shorter (410 – 430 nm) and longer (640 –

182

670 nm) wavelengths (Figure 4A). Judging from the time region and the location of the

ACS Paragon Plus Environment

9

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 21

183

absorption maxima, we tentatively assigned them as M and O intermediates, respectively. These

184

results indicate that elementary reactions are common among the three derivatives of retinal. The

185

M intermediate was formed with the decrease in the initial state absorption soon after the flash

186

excitation and then decayed with formation of the O intermediate. The O intermediate then

187

decayed with the recovery of the initial state and the cyclic reaction was completed (Figures 4B-

188

C). To analyze the reaction kinetics more precisely, the data were fitted with the exponential

189

decay function with a sum of two exponential terms, τ1 for the M intermediate and τ2 for the O

190

intermediate (Figure 4B). From that analysis, we found that the photoreaction kinetics of AO3

191

with A1-retinal or A2-retinal were similar (τ1 = 1.9 ms, τ2 = 119 ms for AO3 with A1-retinal,

192

and τ1 = 1.9 ms, τ2 = 68 ms for AO3 with the A2-retinal) (Figures 4B-C). In contrast, the

193

photoreaction kinetics of AO3 with 14V-A2 was significantly different from those, especially

194

regarding the slow decay of the O intermediate (τ2 = 800 ms) (Figures 4B-C). As shown in

195

Figure 2D, the recovery of the photocurrent for AO3 with 14V-A2 is slower than that of AO3

196

with A1-retinal. The time constant of the recovery of the photocurrent for AO3 with 14V-A2 was

197

estimated to be approx. 400 – 2200 ms, which is consistent with the decay of the O intermediate

198

(800 ms). From these results, we hypothesized that the long-lived O intermediate corresponds to

199

a proton conducting state for the proton channel function. Another explanation is that the

200

rhodopsin undergoes two brunched routes, i.e. one with a fast H+ pumping and another with a

201

slow H+ channel which is not visible in the spectroscopic measurement. Such phenomenon was

202

already observed in the functional conversion of CsR (an algal proton pumping rhodopsin) where

203

passive H+ transfer has much slower photocycle than that of the active proton transfer.21

204

Thus, we demonstrated several characteristic features for AO3 with 14V-A2 as follows; (i)

205

short π-conjugation system on the polyene chain, (ii) characteristic structure around the Schiff

ACS Paragon Plus Environment

10

Page 11 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

206

base region, and (iii) slow recovery of the photocurrent after turning off the light and a long-

207

lived intermediate during the photoreaction. We previously converted AR3 into a light-gated

208

proton channel by three mutations around the chromophore (M128A, G132V and A225T).8 In

209

that study, a slow O-decay was observed with alteration of the hydrogen bond between the PRSB

210

and its counterion.8 Thus, the determinant between the proton pump and the proton channel

211

would be localized around the Schiff base region. We also demonstrated here that, in addition to

212

the protein moiety, the chromophore moiety can be a target to produce a synthetic photoreceptor

213

protein. In order to use our approach (i.e., addition of the synthetic chromophore) for optogenetic

214

purposes, the synthetic chromophore needs to be injected into the organism. Therefore our

215

approach can be directly applied to organisms without retinal synthetic pathway such as

216

Caenorhabditis elegans and some of the bacteria, while the opsin should be protected from

217

naturally occurring retinal for the other organisms. However, as we demonstrated here, when the

218

opsin is overexpressed in the mammalian (murine ND7/23) cells, it successfully incorporates the

219

synthetic retinal chromophore instead of naturally occurring retinal (Figure 2D). Thus our

220

approach would be an alternative choice for optogenetics.

221 222

ACKNOWLEDGMENT

223

This work was financially supported by JSPS KAKENHI Grant Numbers JP15K18519 to TT

224

and JP15H04363, JP15H00878, JP25104005 and JP17H05726 to YS. This research was partially

225

supported by CREST-JST (16815580) and AMED (17933570) to YS, and by PRESTO-JST

226

(JPMJPR1688)

227

ms.com/home.html) for the English language review.

228

ASSOCIATED CONTENT

to

SPT.

We

also

thank

“DASS

Manuscript”

(http://www.dass-

ACS Paragon Plus Environment

11

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 21

229

Supporting Information

230

The Supporting Information is available free of charge on the ACS Publications website at DOI:

231

xxxxxx.

232

Experimental details of chemical synthesis, protein preparation and spectroscopic

233

characterization (PDF).

234

NOTES

235

The authors declare no competing financial interests.

236 237

REFERENCES

238

(1) Ernst, O. P., Lodowski, D. T., Elstner, M., Hegemann, P., Brown, L. S., and Kandori, H.,

239

Microbial and animal rhodopsins: structures, functions, and molecular mechanisms. Chem.

240

Rev. 2014, 114, 126-163.

241 242 243 244 245 246

(2) Kurihara, M., and Sudo, Y., Microbial rhodopsins: wide distribution, rich diversity and great potential. Biophys. Physicobiol. 2015, 12, 121-129. (3) Shichida, Y., and Matsuyama, T., Evolution of opsins and phototransduction. Philos. Trans. R Soc. Lond. B Biol. Sci. 2009, 364, 2881-2895. (4) Spudich, J. L., Yang, C. S., Jung, K. H., and Spudich, E. N., Retinylidene proteins: structures and functions from archaea to humans. Annu. Rev. Cell Dev. Biol. 2000, 16, 365-392.

247

(5) Deisseroth, K., Optogenetics. Nat. Methods. 2011, 8, 26-29.

248

(6) Sudo, Y., and Spudich, J. L., Three strategically placed hydrogen-bonding residues convert a

249

proton pump into a sensory receptor. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 16129-16134.

ACS Paragon Plus Environment

12

Page 13 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

250

(7) Sudo, Y., Okazaki, A., Ono, H., Yagasaki, J., Sugo, S., Kamiya, M., Reissig, L., Inoue, K.,

251

Ihara, K., Kandori, H., Takagi, S., and Hayashi, S., A blue-shifted light-driven proton pump

252

for neural silencing. J. Biol. Chem. 2013, 288, 20624-20632.

253

(8) Inoue, K., Tsukamoto, T., Shimono, K., Suzuki, Y., Miyauchi, S., Hayashi, S., Kandori, H.,

254

and Sudo, Y., Converting a light-driven proton pump into a light-gated proton channel. J. Am.

255

Chem. Soc. 2015, 137, 3291-3299.

256

(9) Kato, H. E., Kamiya, M., Sugo, S., Ito, J., Taniguchi, R., Orito, A., Hirata, K., Inutsuka, A.,

257

Yamanaka, A., Maturana, A. D., Ishitani, R., Sudo, Y., Hayashi, S., and Nureki, O., Atomistic

258

design of microbial opsin-based blue-shifted optogenetics tools. Nat. Commun. 2015, 6, 7177.

259

(10) Nielsen, M. B., Model systems for understanding absorption tuning by opsin proteins.

260

Chem. Soc. Rev. 2009, 38, 913-924.

261

(11) Sudo, Y., Ihara, K., Kobayashi, S., Suzuki, D., Irieda, H., Kikukawa, T., Kandori, H., and

262

Homma, M., A microbial rhodopsin with a unique retinal composition shows both sensory

263

rhodopsin II and bacteriorhodopsin-like properties. J. Biol. Chem. 2011, 286, 5967-5976.

264

(12) Mori, A., Yagasaki, J., Homma, M., Reissig, L., and Sudo, Y., Investigation of the

265

chromophore binding cavity in the 11-cis acceptable microbial rhodopsin MR. Chem. Phys.

266

2013, 419, 23-29.

267

(13) Chow, B. Y., Han, X., Dobry, A. S., Qian, X., Chuong, A. S., Li, M., Henninger, M. A.,

268

Belfort, G. M., Lin, Y., Monahan, P. E., and Boyden, E. S., High-performance genetically

269

targetable optical neural silencing by light-driven proton pumps. Nature 2010, 463, 98-102.

270

(14) Sineshchekov, O. A., Govorunova, E. G., Wang, J., and Spudich, J. L., Enhancement of the

271

long-wavelength sensitivity of optogenetic microbial rhodopsins by 3,4-dehydroretinal.

272

Biochemistry 2012, 51, 4499-4506.

ACS Paragon Plus Environment

13

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 21

273

(15) Bamann, C., Kirsch, T., Nagel, G., and Bamberg, E., Spectral characteristics of the

274

photocycle of channelrhodopsin-2 and its implication for channel function. J. Mol. Biol. 2008,

275

375, 686-694.

276

(16) Feldbauer, K., Zimmermann, D., Pintschovius, V., Spitz, J., Bamann, C., and Bamberg, E.,

277

Channelrhodopsin-2 is a leaky proton pump. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 12317-

278

12322.

279

(17) Palings, I., Pardoen, J. A., van den Berg, E., Winkel, C., Lugtenburg, J., and Mathies, R. A.,

280

Assignment of fingerprint vibrations in the resonance Raman spectra of rhodopsin,

281

isorhodopsin, and bathorhodopsin: implications for chromophore structure and environment.

282

Biochemistry 1987, 26, 2544-2556.

283

(18) Cookingham, R. E., Lewis, A., and Lemley, A. T., A vibrational analysis of rhodopsin and

284

bacteriorhodopsin chromophore analogues: resonance Raman and infrared spectroscopy of

285

chemically modified retinals and Schiff bases. Biochemistry 1978, 17, 4699-4711.

286

(19) Baasov, T., Friedman, N., and Sheves, M., Factors affecting the C = N stretching in

287

protonated retinal Schiff base: a model study for bacteriorhodopsin and visual pigments.

288

Biochemistry 1987, 26, 3210-3217.

289

(20) Kanehara, K., Yoshizawa, S., Tsukamoto, T., and Sudo, Y., A phylogenetically distinctive

290

and extremely heat stable light-driven proton pump from the eubacterium Rubrobacter

291

xylanophilus DSM 9941T. Sci. Rep. 2017, 7, 44427.

292 293

(21) Vogt, A., Guo, Y., Tsunoda, S. P., Kateriya, S., Elstner, M., and Hegemann, P., Conversion of a light-driven proton pump into a light-gated ion channel. Sci. Rep. 2015, 5, 16450.

ACS Paragon Plus Environment

14

Page 15 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

294 295

Figure 1. Expression of AO3 with vinylene derivatives. (A) Chemical structures of natural

296

retinals (A1- and A2-) and three newly synthesized vinylene derivatives (6V-A2, 10V-A2 and

297

14V-A2). Absorption maxima (λmax) of A1-retinal, A2-retinal and the three synthesized

298

derivatives in EtOH solution are shown in parentheses. (B) Schematic of an outward proton

299

pump. All-trans A1-retinal binds to the cognate apoprotein opsin via the protonated Schiff base

300

linkage with the conserved lysine residue. EC and CP indicate extracellular side and cytoplasmic

301

side, respectively. (C) Visible color of E. coli BL21(DE3) cells expressing AO3 with natural or

302

synthesized derivatives of retinal.

ACS Paragon Plus Environment

15

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 21

303 304

Figure 2. Light-induced proton transport activity in AO3 with A1-retinal, A2-retinal, 6V-

305

A2, 10V-A2 or 14V-A2. (A) Light-induced pH changes of E. coli cells expressing AO3 with

306

A1-retinal, A2-retinal, 6V-A2, 10V-A2 and 14V-A2. The cell suspensions were illuminated with

307

light (9-12 mW/cm2) for 3 min. The wavelengths of light were roughly chosen from the visible

308

color of the cells. The thick and thin gray lines indicate pH changes in the absence or presence of

309

CCCP (10 µM), respectively. (B) Absorption spectra of the purified proteins in a buffer

310

containing 50 mM Tris-HCl (pH 7.0), 1 M NaCl and 0.05 % DDM. (C) Action spectra of AO3

311

with A1-retinal, A2-retinal or 14V-A2 with offsets. The initial slope amplitudes of the light-

312

induced pH changes of E. coli cell suspensions are plotted against varying wavelengths of light

313

(6 mW/cm2). Data points represent the averages of 3 independent experiments; error bars

314

represent standard deviations (SD). Absorption spectra were superimposed into the figure (solid

ACS Paragon Plus Environment

16

Page 17 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

315

lines). (D) Whole cell patch-clamp recordings of the ion transport activities of AO3 with A1-

316

retinal (black, left panel) or 14V-A2 (blue, right) in ND7/23 cells. Representative current traces

317

of cells expressing AO3 with A1-retinal or 14V-A2 are shown. The holding potential was kept at

318

+20 mV. Upper and lower panels show traces at extracellular pHo of 7.2 and 4.5, respectively.

319

The 580 nm light was illuminated during the time indicated by the grey bars on the traces. (E, F)

320

Current-voltage relationship (I-V plot) of the photocurrent of AO3 with (E) A1-retinal (black) or

321

(F) 14V-A2 (blue) at pHo of 7.2 (filled circles) and 4.5 (open circles). For AO3 with A1-retinal

322

(panel E), the current amplitude was normalized to the condition of pHo 7.2 at 0 mV as 1.0. Error

323

bars represent SD (n = 4 for pHo 7.2 and 3 for pHo 4.5). For AO3 with 14V-A2 (panel F), the

324

current amplitude was normalized to the condition of pHo 7.2 at -80 mV as 1.0. Error bars

325

represent SD (n = 3 for pHo 7.2 and 5 for pHo 4.5).

ACS Paragon Plus Environment

17

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 21

326 327

Figure 3. Photochemical properties of AO3 with A1-retinal, A2-retinal or 14V-A2. (A)

328

Absorption spectra of AO3 with A1-retinal ranging pH7 to pH2. (B) Absorption spectra of AO3

329

with A2-retinal ranging pH7 to pH2. (C) Absorption spectra of AO3 with 14V-A2 ranging pH7

330

to pH3. (D) Estimation of the pKa of the counterion Asp95 by pH-induced absorbance change of

331

AO3 with A1-retinal (black open circle), A2-retinal (red) or 14V-A2 (blue). Solid lines represent

332

fitting curves by the Henderson-Hasselbalch function with a single pKa. The experiments were

333

performed at room temperature (ca. 25˚C). (E) Resonance Raman spectra of AO3 with A1-

334

retinal (black line), A2-retinal (red) or 14V-A2 (blue). The solid and dotted lines indicate the

ACS Paragon Plus Environment

18

Page 19 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

335

spectra of retinals hydrated with H2O or D2O, respectively. Numbers marked by asterisks are

336

values for the D2O sample. Expanded views of the resonance Raman spectra of AO3 with A1-

337

retinal, A2-retinal and 14V-A2 were also represented as insets. The probe wavelength was 532

338

nm and the concentration of the sample was approximately 20 µM. The experiments were

339

performed at approximately 20˚C. The data for AO3 with A2-retinal or 14V-A2 were scaled by

340

2.2 and 1.3, respectively, for comparison.

ACS Paragon Plus Environment

19

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 21

341

342 343

Figure 4. Photochemical kinetics of AO3 with A1-retinal, A2-retinal or 14V-A2. (A) Time-

344

resolved transient absorption spectra of AO3 with A1-retinal (upper panel), A2-retinal (middle

345

panel) or 14V-A2 (lower panel) against wavelength ranging from t = 0.80 msec to 8110 msec

346

time frame. (B) Time-resolved transient absorption changes of AO3 with A1-retinal (upper

347

panel), A2-retinal (middle panel) or 14V-A2 (lower panel) against time. The dotted grey lines

348

represent the fitting curves with the sum of two exponential terms. The temperature was kept at

349

15˚C. (C) A model for the photoreaction. Subscribed numbers indicate the absorption maxima of

350

each state.

ACS Paragon Plus Environment

20

Page 21 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Production of a light-gated proton channel by replacing the chromophore 50x50mm (300 x 300 DPI)

ACS Paragon Plus Environment