J. Am. Chem. SOC.1991, 113, 2758-2760
2158
Construction of a Light-Activated Protein by Unnatural Amino Acid Mutagenesis
Scheme I
David Mendel, Jonathan A. Ellman, and Peter G.Schultz*
Department of Chemistry, University of California Berkeley, California 94720 Center for Advanced Materials Lawrence Berkeley Laboratory One Cyclotron Road Berkeley, California 94720 Received December 18, 1990
= ROMP Polymer =Low Dendty SiOB Network J
organic polymer. Contrast between the two phases can be best achieved by etching away (oxygen plasma)I2 the organic polymer to leave behind the textured glass surface, revealing cavities left Low molecular weight caged substances, inactive precursor by the polymer. Comparison of an etched SIPN composite with molecules that can be activated photochemically, are useful tools a transparent composite made from a preformed polymer (cellulose for biochemical studies.14 Photolabile acyl enzyme adducts are acetate) clearly displays a smaller domain size for SIPN comalso of interest in triggering enzymatic reaction^.^ We now report posites over those materials derived from preformed polymers a general approach to the construction of caged proteins based (Figure 1). on methodology that allows site-specific incorporation of unnatural A significant drawback associated with the sol-gel process is amino acids into This development should make removal of the cosolvent, excess water, and liberated alcohol. possible a broad range of time-resolved experiments relevant to Xerogels routinely shrink 70-80% during the drying p r o c e ~ s , ~ ~ ~protein ~ folding, protein-protein and protein-ligand interactions, which precludes molding processes and can introduce a high degree catalytic mechanisms, and protein conformational studies. Here of stress within materials. Because of this shrinkage, gels must we describe the construction of a photoactivatable phage T4 be dried at unreasonably slow rates to avoid cracking and delysozyme (T4L) containing an aspartyl /3-nitrobenzyl ester (NBformation of the geL5 In an effort to overcome the problems Asp) in the active site. associated with xerogel formation, we have synthesized tetraT4L is a stable, well-characterized enzyme whose lysis of alkoxysilanes from SiC14 and the strained, cyclic alkenols 2 and Escherichia coli cells provides a convenient and sensitive assay 5.14 By employing polymerizable monomers such as monomers for catalytic activity.* Aspartic acid 20 (Asp 20) and glutamic 2,3,4, or 5 as the cosolvent, the tetraalkoxysilane derivative, and acid 11 (Glu 11) oppose one another across the binding cleft floor a stoichiometric quantity of water, all components of the composite and are essential for catalytic It has been proposed solution contribute to either the Si02 network or the organic that Glu 11 of T4L donates a proton to the interglycosidic oxygen polymer. Since both the cosolvent and the liberated alcohol of P( 1-.4)-linked NAM-NAG residues of the cell wall and that polymerize, gel drying is unnecessary and no gel shrinkage occurs the incipient oxonium ion decomposes to give a truncated poly(Scheme I). saccharide and a carbocation which is stabilized by Asp 20.1° An Since the nonshrinking formulations are essentially bulk poaspartyl P-nitrobenzyl ester was therefore introduced at position lymerizations, kinetic studies of the ROMP rates and condensation 20 to produce a catalytically inactive (caged) lysozyme. Upon rates at high monomer concentrations were studied in order to irradiation, nitrobenzyl esters are known to undergo rapid (on the verify simultaneous completion of both reactions. At high conorder of millisecondsll) conversion to the free acid plus 0centrations, the polymerization of alcohol 5 shows first-order nitrosobenzaldehyde. Irradiation of the inactive, NB-Asp-cons-l). At higher behavior between 4.0 and 7.0 M ( k = 1.9 X taining lysozyme thus generates a fully active protein. concentrations (pertinent for the bulk polymerization of 6 ) , sigBecause suppression of the Asp 20 amber mutant is carried out nificant deviation toward faster rates is observed. Consistent with in vitro, it was necessary to verify that protein synthesized in vitro these observations, the ROMP of 5 is greater than 90% complete is the same as protein synthesized in vivo. T4LI2 was expressed after 1.5 min. It is most convenient to match the sol-gel rates and purified to homogeneity from the cell-free coupled tranwith these ROMP rates by adjusting the concentration of the scription-translation system of ZubayI3 programmed with the condensation catalyst (NaF). For example, in the absence of ROMP catalysts, the condensation of compound 6 with stoiAuthor to whom correspondence should be addressed. chiometric water can be varied from several seconds to several ( I ) (a) Schlichting, I.; et al. Nature 1990, 345, 309. (b) Schlichting, I.; days by simply adjusting the N a F concentration. To match the et al. Proc. Nail. Acad. Sci. U.S.A. 1989, 86, 7687. (2) (a) Blatt, M. R.; Thiel, G.; Trentham, D. R. Nature 1990, 346, 766. above ROMP rates, gel times of 1.5-2.0 min at 60 OC can be (b) Parker, I.; Ivorra, I. Science 1990, 250,977. (c) Adams, S. R.; et ai. J . achieved by using N a F solutions near 50 mM. Significant deAm. Chem. SOC.1988, 110, 3212. (d) Adams, S.R.; Kao, J. P. Y.; Tsien, viations from these matched rates result in systems that approach R. Y.J . Am. Chem. SOC.1989, I 11, 7957. the homopolymerization limits: uncontrolled polymer precipitation (3) Gilroy, S.;Read, N. D.;Trewavas, A. J. 1990, 346, 769. (4) Wilcox, M.; et al. J . Org. Chem. 1990, 55, 1585. when the ROMP rate is greater than the condensation rate, or (5) (a) Stcddard, B. L.; Bruhnke, J.; Porter, N.; Ringe, D.;Petsko, G. A. brittle glasses which shrink (due to unreacted monomer evapoBiochemistry 1990, 29,4871. (b) Stoddard, B. L.; Bruhnke, J. L.; Koenigs, ration) when the condensation rate is much greater than the P.; Porter, N.; Ringe, D.; Petsko, G. A. Biochemistry 1990, 29, 8042. ROMP rate. Under ideal reaction conditions, a transparent (6) (a) Noren, C. J.; et al. Science 1989, 244, 182. (b) Ellman, J. A.; et. al. Methods Enzymol., in press. glass-polymer composite is obtained with no observable shrinkage.
Acknowledgment. This work was supported by University of California 'Startup Funds", the Center for Advanced Materials, Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, and E. I. du Pont de Nemours and Company. M.W.E. gratefully acknowledges the DOED for a graduate fellowship. (12) Etching performed with a Plasmod oxygen plasma etcher, courtesy of Dr. Donald Scales, California State Department of Public Health, Berkeley, CA. (13) Brinker, C. J.; Scherer, G. W. Sol-Gel Science. The Physics and Chemistry of Sol-Gel Processing, Academic Press: New York, 1990. (14) Ebelmen, J. J. Justus Liebigs Ann. Chem. 1846,57, 331.
(7) Recently a similar approach has been used to incorporate unnatural amino acids into peptides; see: Bain, J. D.; et al. J . Am. Chem. Soc. 1989, 1 1 1 , 8013. (8) (a) Tsugita, A,; et al. J . Biol. Chem. 1968,243, 391. (b) Tsugita, A. In The Enzymes; Boyer, P. D., Ed.; Academic Press: New York, 1971; Vol. 3, pp 343-41 1 and references therein. (9) Weaver, L. H.; Matthews, B. W. J. Mol. Biol. 1987, 193, 189. (10) Dao-Pin, S.; Liao, D.-I.; Remington, S. J. Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 5361 and references therein. (1 1) Pillai, V. N. R. Synthesis 1990, 1. (12) The cysteine-free mutant T4L (C54T, C97A) was used in these studies because it is virtually identical with the wild-type protein in structure and activity, but does not suffer oxidative degradation; see: Perry, L. J.; Wetzel, R. Biochemistry 1986, 25, 733. (13) (a) Zubay, G. Annu. Rev. Genet. 1973, 7 , 267. (b) Collins, J. Gene 1979, 6, 29. (c) Pratt, J. In Transcription and Translation: A Practical Approach; Hames, B. D.,Higgins, S. J., Eds.; IRL Press: Oxford, 1984; pp 179-209.
0002-786319111513-2758%02.50/0 0 1991 American Chemical Society
Communications to the Editor
J . Am. Chem. Soc., Vol. 113, No. 7. I991
2759
I
I
I
-
43.0
29.0 0
1 -
1
18.4
-
14.3
-
6.2
-
2.3-3.4
Figure 1. Course of T4 lysozyme purification (adapted from ref 12) from cell-free E. coli extract analyzed by 15% SDS-PAGE. Lanes: 1. crude polyethylenimine lysate supernatant; 2, DEAE- and CM-cellulose tandem column wash: 3, pooled T4L-active fractions from NaCl gradient on CM-cellulose column; 4, purified in vitro produced T4L after cationexchange chromatography (Pharmacia Mono s);5 , T4L purified from IPTG-induced E. coli cells harboring the plasmid pHSe54.97.TA; 6, molecular weight standards. In vitro protein synthesis reactions were as described in refs 6 and 13.
plasmid pHSe54.97.TA which encodes T4L behind the twin lac promoter (Figure 1). Both in vitro and in vivo preparations of T4L have the same chromatographic properties and apparent molecular mass of approximately 18 700 Da (daltons). More importantly, both preparations display the same kinetics toward lysis of E. coli strain Nap IVI4 cells at three different substrate concentrations (data not shown). The amber mutant jD20 TAG (pT4LD20am)l of T4L was constructcd via the Eckstein method.Is When the in vitro protein synthesis system is programmed with plasmid pT4LD2Oam in the absence of supprcssor tRNA, no synthesis of T4L is secn as determined by polyacrylamide gel electrophoresis of [ 3sS]methioninc-labclcd proteins (lane 2, Figure 3). Based on scintillation counting of gel slices, less than 1.55% readthrough of the amber codon is oberved at 2 mM added Mg2+. This control shows that the level of translation of the amber codon by noncognate tRNAs is insignificant under the conditions employed. Addition of 7.5 pg of full-length unacylated suppressor tRNAcuA (Figure 2) to the pT4LD20am-programmed reaction again results in less than I .5% readthrough at 2 mM added Mg2+ (Figure 3. lane 3). This control insures that protein produced from the amber mutant will not bc hctcrogencous due to partial incorporation of the natural 20 amino acids. In accord with the lack of a full-length T4L band, ncithcr of these two control reactions yielded any lytic activity. In contrast, in vitro synthesis reactions primed with plasmid pHSe54.97.TA produced 40-50 pg of enzyme/mL of in vitro reaction mixture (lane 1, Figure 3). The wild-type in vitro reaction hydrolyzes E. coli cells at rates of approximately 4 ODdCOnm units/min per 2 p L of in vitro upe ern at ant.'^
0
2
Figure 2. Atninoacyl suppressor tRNAcuA construction scheme. Yeast tRUAPhccontaining CUA at the anticodon loop and missing the 3’ terminal CA residues (tRNAcuA (-CA)) was constructed according to Bruce and Uhlenbeck16 using synthetic rCUAA.” NVOC-protected (nitrovertryloxycarbnyl) or BPOC-protected” (biphenylisopropyloxycarbonyl) aminoacyl pdCpA was synthesized and purified according to ref 19 and was then ligated to tRNAcuA ( 315 nm (Oriel Hg-Xe arc lamp, 1000 W) restored lytic activity to the NB-Asp-suppressed T4L. The irradiated material yielded 32 f 3% of the activity of the wild-type enzyme, agreeing very closely with suppression levels based on scintillation counting of gel bands. These results show that NB-Asp-tRNAcuA efficiently suppresses pT4LD2Oam to produce mutant T4L with latent activity that can be released by rapid photolysis. Moreover, virtually all of the caged protein is converted to the active form. We are currently extending this methodology to other amino acids such as serine, tyrosine, lysine, and cysteine located at both internal and external sites in a number of proteins.
Acknowledgment. We thank the Matthews and Dahlquist groups and Laurence McIntosh of the University of Oregon for providing the pHSe expression vectors and maps and Nora Linderoth for the Nap IV strain. This work was funded by the Procter and Gamble UERP program, O N R Grant NOOO14-87-K-0256 (J.A.E.), and by the Director, Office of Energy Research, Office of Basic Energy Sciences, Division of Material Sciences and also by the Division of Energy Biosciences of the US.Department of Energy (DE-AC03-76SF00098) (D.M.). D.M. was supported by American Cancer Society postdoctoral fellowship PF-4014 and J.A.E. by National Science Foundation postdoctoral fellowship CHE-8907488. P.G.S. is a W. M. Keck Foundation Investigator.
Second-Sphere Coordination of Transition-Metal Complexes by Calix[4]arenes Jerry L. Atwood,* G. William Orr, Fumio Hamada, Rebecca L. Vincent, Simon G. Bott, and Kerry D. Robinson Department of Chemistry, University of Alabama Tuscaloosa. Alabama 35487 Received December 17, I990 Second-sphere coordination has been defined by Stoddart as the 'non-covalent bonding of chemical entities to the first coordination sphere of a transition metal complex."lb The importance of such systems for biological receptorsz4 and for supramolecular assemblies5 has been noted.' The use of crown ethers as second-sphere ligands via hydrogen bonding is well Numerous studies of cyclodextrins coordinated to transition-metal complexes have also appeared.1*7-8-14 However, even though (1) (a) Colquhoun, H. M.; Stoddart, J. F.; Williams, D. J. Angew. Chem., Inr. Ed. Engl. 1988, 27, 1986. (b) Alston, D. R.; Ashton, P. R.; Lilley, T. H.; Stoddart, J. F.; Zarzycki, R.; Slawin, A. M.Z.; Williams, D. J. Curhhydr. Res. 1989, 192, 259. (2) Shaw, J.; Everett, G. W. Inorg. Chem. 1985, 24, 1917. (3) Gessner, R. V.; Quigley, G.J.; Wang, A. H.-J.; van der Marel, G. A,; van Boom, J. H.; Rich, A. Biochemisrry 1985, 24, 237. (4) Sherman, S. E.; Lippard, S. J. Chem. Rev. 1987, 87, 1153. (5) Lehn, J.-M. Angew. Chem., Ini. Ed. Engl. 1988, 27, 89. (6) Colquhoun, H. M.;Doughty, S. M.; Slawin, A. M.Z.; Stoddart, J. F.; Williams, D. J. Angew. Chem., Inr. Ed. Engl. 1985, 24, 135. (7) Alston, D. R.; Slawin, A. M. Z.; Stoddart, J. F.;Williams, D. J. Angew. Chem., Inr. Ed. Engl. 1985, 24, 786. (8) Joh, T.; Harada, A,; Takahashi, S . Mem. Insr. Sci. Ind. Res., Osaka Univ. 1989, 46, 37. (9) Alston, D. R.; Slawin. A. M. Z.; Stoddart, J. F.; Williams, D. J.; Zarzycki, R. Angew. Chem., In?. Ed. Engl. 1988, 27, 1184. (IO) Alston, D. R.; Lilley, T. H.; Stoddart, J. F. J. Chem. Sac., Chem. Commun. 1985, 1600. (11) Kobayashi, N.; Opallo, M. J . Chem. SOC.,Chem. Commun.1990. 477.
0002-7863/91/1513-2760$02.50/0
Figure 1. Structure of [(H20)5Ni(NC,H,)J2(Na) [calix[4]arene sulfonate].3.5H20 illustrating the bilayer arrangement of the calixarenes, the intercalation into the bilayer, and the second-sphere coordination of the transition-metal complex. The two independent Ni-N distances are 2.08 ( I ) A, and the Ni-O(water) lengths range from 2.05 (1) to 2.18 (1) A.
calixarenes are one of the most readily accessible three-dimensional macrocycles15 and are under intense investigation by numerous groups,'6-18no examples of second-sphere coordination have a p peared. We report herein that the hydrophobic cavity of [calix[4]arene sulfonateI5- can be employed for such second-sphere coordination. In addition, the title compounds also exhibit a new type of intercalation behavior with regard to the bilayer assembly of the c a l i x a r e n e ~ . ~ ~ - ~ ~ Three equivalents of the deep blue Ni(NC5H5)3(N03)z22z3 was dissolved in deionized water (with hydrolysis) to which 1 equiv of Na5[calix[4]arenes ~ l f o n a t ehad ] ~ ~been added. The resultant pale blue solution yielded pale blue crystals of [(Hz0)5Ni(NC5H5)],(Na)[calix[4]arene sulfonate].3.5Hz0 upon slow evaporation in a vacuum desiccator. The structurez4 of the complex is shown in Figure 1. There are two different [(Hz0)5Ni(NC5H5)]z+cations in the assembly. In one the hydrophobic pyridine ring is complexed by the hydrophobic cavity of the calixarene. The depth of penetration of the aromatic moiety into the cavity may be measured by the distance of the centroid of the pyridine ring from the plane of the calixarene CHz carbon atoms. For the nickel complex the value (12) Klingert, B.; Rihs, G.Organomerallics 1990, 9, 1135. (13) Harada, A.; Hu, Y.; Yamamoto, S.;Takahashi, S. J . Chem. Soc., Dalron Trans. 1988,129. (14) Ashton, P. R.; Stoddart, J. F.; Zarzycki, R. Tetrahedron h i . 1988, 29, 2103. (15) Gutsche, C. D. Culixurenes; Royal Soc. Chem.: Cambridge, 1989. (16) Calixarenes; B6hmer, V., Vicens, J., Eds.; Kluwer: Dordrecht, 1990. (17) Gutsche, C. D. In Inclusion Compounds; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Eds.; Oxford University Press: Oxford; Vol. 4, 1991; pp 27-63. (18) Andreetti, G. D.; Ugouoli, F.; Ungaro, R.; Pochini, A. In Inclusion
Compounds; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Eds.; Oxford University Press: Oxford; Vol. 4, 1991; pp 64-127. (19) Coleman, A. W.; Bott, S. G.; Morley, S. D.; Means, C. M.; Robinson, K. D.; Zhang, H.; Atwood, J. L. Angew. Chem., Inr. Ed. Engl. 1988,27,1361. (20) Bott, S. G.;Coleman, A. W.; Atwood, J. L. J. Am. Chem. Soc. 1988,
110, 610. (21) Atwood, J. L.; Coleman, A. W.; Zhang, H.; Bott, S. G.J . Inclusion Phenom. Mol. Recognit. Chem. 1989, 7, 203. (22) Rosenthal, M. R.; Drago, R. S. Inorg. Chem. 1965, 4, 840. (23) Atwood, J. L.; Bott, S. G.;Vincent, R. L. J . Crystallogr. Specfrosc. Res. 1990, 20, 631. (24) [(H20),Ni(NCsHs)],(Na)[calix[4]arene sulfonate].3.5H20 crystallizes in the triclinic space group PI with u = 12.487 (4) A, b = 14.281 (2) A, c = 15.055 ( 5 ) A, a = 85.66 (2)", 9, = 80.07 (2)". y = 80.48 (2)O. and Daw = 1.64 g ~ m for ' ~Z = 2. Refinement based on 2441 observed reflections led to a final R value of 0.066.
0 1991 American Chemical Society
