Cadmium Chelation by Bacterial Teichoic Acid from Solid-State

Biomacromolecules 2010, 11, 333–340

333

Cadmium Chelation by Bacterial Teichoic Acid from Solid-State Nuclear Magnetic Resonance Spectroscopy Jeffrey L. Halye and Charles V. Rice* Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Room 208, Norman, Oklahoma 73019 Received May 2, 2009; Revised Manuscript Received December 11, 2009

An effective means of studying biological metal chemistry is through the use of cadmium NMR to probe the interaction between biomolecules, such as proteins and peptides, with divalent metals, such as zinc, copper, magnesium, or calcium. Gram-positive bacteria, such as S. aureus and B. subtilis, have peptidoglycan cell walls that contain teichoic acids, a poly(phosphodiester) biopolymer used for, among other things, metal chelation. Previous solid-state NMR and XAFS studies have shown that the cadmium ion binds in a bidentate manner to the phosphoryl centers of the dried teichoic acid backbone at physiological pH. However, current studies indicate that, when hydrated and at the low concentrations typically found in nature, the cadmium ions and phosphoryl sites interact through an extended solvent-separated ion pairing. These data reveal two unequal P-Cd interactions at distances of 4.2 and 4.9 Å set approximately 180° from each other in a linear arrangement.

Introduction The cell wall of Gram-positive bacteria is mainly composed of peptidoglycan (peptide cross-linked disaccharide polymers) and teichoic acids (long phosphodiester polymers), which are essential to bacterial health. Teichoic acids are suggested to participate in several different aspects of bacterial survival, one being the coordination of metal cations. Of the different functional groups present in teichoic acids (phosphate, alanine, N-acetylglucosamine, hydroxyl, Figure 1), the phosphates are the primary chelation site and have been the subject of numerous investigations into the metal binding chemistry. The need for teichoic acids to assist with Mg2+ uptake was demonstrated by studies of B. subtilis bacteria grown in low magnesium concentrations.1,2 These bacteria demonstrated significant increases in the amount of teichoic acids produced in the cell wall to maximize metal binding. It is well-known that bacteria, especially the Gram-positive variety, carry an enormous capacity for metal chelation.3 Studies have also shown that both the carboxyl sites of peptidoglycan and the phosphoryl sites of teichoic acid show affinity for metal chelation over a broad range of pH values.4 However, little is currently known about the exact mechanism in which the bacteria binds and intercalates these metal ions. The inherent difficulty lies in the ability to obtain in situ structural information about the binding environment between biologically relevant divalent metal cations and their associated binding sites. The vast majority of these interactions are based on a specific binding affinity that allows for rapid exchange processes to occur in solution, distorting the obtainable data. However, the binding process, while in solid phase, is irreversible, allowing for measurements over long periods of time. Therefore, the use of nuclear magnetic resonance (NMR) active nuclei and solid-state NMR techniques combine to form a powerful tool for these studies. Although limited indirect studies of metal/phosphate interactions have led to meaningful information, a direct observation of the metal binding environment by NMR spectroscopy would provide a great deal of insight. However, due to the NMR * To whom correspondence should be addressed. E-mail: [email protected].

characteristics of 25Mg and 43Ca, this type of study is nearly impossible using current techniques. Therein lies the motivation for the current study; because cadmium retains a d10 valence electron structure regardless of the ligands bound to it, the pseudo 2s electron configuration allow for its use in imitating the physical and reactive properties of divalent metals such as calcium. Cadmium and calcium share an extremely similar ionic radius, 0.95 and 1.00 Å, respectively, allowing for calcium specific binding studies to be performed through the use of cadmium. In fact, there have been many studies that have derived indirect data regarding calcium complexation with proteins and enzymes through the use of a cadmium probe.5-8 Our own studies show that the 31P NMR spectra of the teichoic acid backbone chelated to magnesium, calcium, and cadmium show nearly identical isotropic chemical shifts and absolutely identical tensor data.9 Our experimental data show that the use of a cadmium probe can be extended to magnesium:phosphate complexation studies as well. Indeed, there have been several other studies, ranging from liquid state protein interaction studies to tensor analyses of cadmium bound to inorganic complexes, that have utilized the cadmium-113 nucleus to model the binding chemistry of other inactive nuclei, such as magnesium, calcium, copper, or zinc.8,10-16 Teichoic acid extends past the cell wall where it can bind metals from the extracellular fluid. The resulting chelation of cations reduces electrostatic repulsion between neighboring phosphate groups. Stabilization in this manner has been observed in the phosphate groups of nucleic acids and lipid membranes.17-19 Teichoic acid is a major component (30-60% by mass) of the cell walls20-22 and is found as both a lipid-anchored teichoic acid (lipoteichoic acid, LTA) and a wall-anchored teichoic acid (WTA).20-22 The disaccharide headgroup of WTA is covalently attached to the peptidoglycan cell wall,22 while LTA is attached via a lipid chain anchored in the phospholipid membrane. Both LTA and WTA contain disaccharide D-glucose head groups with a poly(phosphodiester) chain (Figure 1A-C) extending out past the cell wall.22,23 Depending on the bacterial strain, the backbone of WTA is either the poly(glycerol phosphate), Figure 1B, or the poly(ribitol phosphate), Figure 1C. The basic chemical

10.1021/bm9010479  2010 American Chemical Society Published on Web 01/13/2010

334

Biomacromolecules, Vol. 11, No. 2, 2010

Halye and Rice

Figure 1. Diverse chemical structure of teichoic acids found in the cell wall of Gram-positive bacteria. The polyphosphate backbone is very long, with 20-50 repeat units dependent upon the species of bacteria. The different constituents of teichoic acid facilitate chemical interactions with various ionic species, water, and the cell wall peptidoglycan. LTA is identical for S. aureus and B. subtilis. However, while WTA of S. aureus has a poly(ribitol phosphate) backbone, WTA from B. subtilis has a poly(glycerol phosphate) backbone with glucose in place of N-acetylglucosamine.

structure of teichoic acids has previously been determined from proton and carbon liquid-state NMR.24-30 The poly(phosphodiester) chain has 20-50 repeat units,22,25,27,29,31 decorated with alanyl, sugar, and hydroxyl groups.31-33 For S. aureus at pH < 7, the D-alanine groups are cationic, the phosphodiesters are anionic, and both the N-acetylglucosamine and hydroxyls are neutral.31-33 This results in incomplete charge neutralization,34 which allows teichoic acid to form ionic bonds with surrounding fluids, dissolved ions, and substrates as well as possible intramolecular contact-ion pairs between the D-alanine and phosphate groups. A recent solid-state nuclear magnetic resonance (SSNMR) and density functional theory (DFT) computational study completed by our research group shows that the chelation of Mg2+ by teichoic acid is accomplished in a bidentate manner at high metal concentration and physiological pH.9 Here we demonstrate the complexation of Cd2+ with teichoic acid as a bidentate process as well. In recent literature, the binding of Cd2+ to carboxyl and phosphoryl sites within the peptidoglycan and teichoic acid polymer has been studied by Fein et al.4 In these studies, X-ray absorption fine structure spectroscopy (XAFS) and molecular simulations were used to determine the binding motif of Cd2+ at various pH values. The data supported a conclusion that, due to the pKa values for phosphoryl centers, Cd2+ bonded in a monodentate fashion at low pH but became bidentate at human physiological conditions. This supports our current phosphorus SSNMR and computational data but also challenges the current paradigm developed by Baddiley et al. in 1973.35 In contrast to the prior studies, distance measurements with rotational-echo double-resonance (REDOR) show that chelation by phosphate occurs in a solvent-separated, outer sphere, manner.

Experimental Section Sample Preparation. Staphylococcus aureus lipoteichoic acid (LTA) was purchased as a lyophilized powder from InvivoGen. This material was isolated by the manufacturer via butanol extraction, purified with hydrophobic interaction chromatography (HIC), and residual metals removed by dialysis with EDTA. Nonisotopically labeled MgCl2, CaCl2, and CdCl2 samples were prepared by dissolving the chloride salts into sterile water at 60, 60, and 120 mM concentrations, respectively. A total of 1 mL of each was used to dissolve a separate 15 mg LTA sample, subsequently vortexed, sealed for 24 h, and lyophilized. Although the cadmium-113 nucleus seems to be much more popular in published reports, the cadmium-111 isotope also possesses a 1/2 spin nucleus that is almost identical in both natural abundance as well as NMR sensitivity. 111CdCl2 was prepared locally from previously obtained >95% isotopically labeled 111CdO by acidification with 0.1 M HCl, filtration, and subsequent lyophilization to remove any remaining acid. 3.8 mg of 111CdCl2 was dissolved into 1 mL of sterile water, which was in turn used to dissolve 15 mg of LTA. Samples were vortexed and sealed for 24 h at room temperature. The sample was then lyophilized prior to packing into the NMR rotor. NMR Experiments. Solid-state NMR experiments were performed using a 300 MHz Varian UnityInova three-channel NMR spectrometer and a 2.0 mm, three-channel, magic-angle-spinning NMR probe (Revolution NMR design). 31P CP-MAS experiments of LTA samples were collected with 20000 scans, 2 s repetition rate, 3000 Hz spinning rate, and a contact time of 2000 µs with an 1H rf power level of 50 kHz for cross-polarization spin-lock and for 1H decoupling. Drive and bearing gas were provided by dry compressed air. 31P chemical shift data were referenced to an external standard of 85% phosphoric acid (0 ppm). The temperature was 25 °C. Data acquisition and spectral analyses were accomplished using the VnmrJ1.1D (Varian, Inc.) and the Herzfeld-Berger Analysis software package,36 respectively.

Cd2+ Chelation by Teichoic Acids


Figure 2. REDOR pulse sequences associated with the S0 (left) and Sr (right) spectra. The train of rotor-synchronized π pulses on the channel serves to reintroduce the heteronuclear dipolar coupling interactions normally averaged away by MAS.

REDOR data were collected using a sample spinning rate of 10 kHz, a cross-polarization contact time of 2000 µs, and 1H decoupling at a radio frequency (rf) power level of 50 kHz. The rf powers for the 31P and 111Cd channels were 50 and 86 kHz, respectively. The XY-8 phase cycling scheme was used on both the 31P and 111Cd channels.37 S0 and Sr spectra were recorded at intervals of eight rotor cycles from 8 to 160 and then in intervals of 16 rotor cycles from 176 to 320. Eight rotor interval spectra were collected with 1000 scans and 16 rotor interval spectra were collected with 2000 scans, both at a 2 s recycle time. REDOR is used in solid-state NMR to measure dipole-dipole coupling between heteronuclei.38,39 Detailed mathematical and pictorial descriptions of REDOR have been reported.37-40 The REDOR experiment requires the acquisition of two NMR spectra collected under MAS conditions (Figure 2). The first spectrum, labeled S0, is collected using decoupling (1H) and observe spin (denoted S-spin, 31P) rf pulses only. Between the pulses and the data acquisition, dipolar-coupling effects are averaged away by the use of MAS, and the signals have full intensity. A second spectrum, labeled Sr, is collected using identical 1 H and 31P pulses, with rf pulses applied to another nucleus (denoted the I-spin, 111Cd for these experiments) at selected intervals. The I-spin pulses reintroduce the dipolar interaction that otherwise would be averaged away by MAS. The dipole-dipole interaction causes a transverse dephasing of the magnetization, reducing the signal intensity. Although the I-spin rf pulses that cause dephasing each have a fixed duration, the amount of transverse dephasing can be increased by using more pulses, which decreases Sr. The distance between 31P and 111Cd can be found by relating the intensity of Sr to the dephasing time. However, other T2 processes may cause additional signal loss, affecting both S0 and Sr, so their effect is corrected for by taking the difference between Sr and S0 and then dividing by S0. A plot of ∆S/S0 versus dephasing time yields the REDOR dephasing curve. The SIMPSON program41 calculates a theoretical dephasing curve based on the nuclear spin system and the dipolar-coupling constants. The distance between the interacting spins can be extracted from the strength of the dipole-dipole coupling using eq 1,

D ) (µ0p/4π)(γIγS /r3)

(1)

where D is the dipolar-coupling constant, µ0 is the permittivity of free space, γI is the magnetogyric ratio of the dephasing nuclei (111Cd), γS is the magnetogyric ratio of the observe nuclei (31P), and r is the internuclear distance. Dipolar-coupling constants were determined from SIMPSON41 simulations that generate theoretical REDOR dephasing curves based on internuclear distance approximations.

Results and Discussion Solid-state nuclear magnetic resonance spectroscopy experiments were performed on teichoic acid with various divalent cations bound. Phosphorus-31 principal tensor components were extracted via Herzfeld-Berger Analysis software,36 which were

335

111

Cd

then utilized in eqs 2a-c to calculate isotropic chemical shift (δiso), reduced chemical shift anisotropy (∆δ) and

|δzz - δiso | g |δxx - δiso | g |δyy - δiso | δiso ) (δxx + δyy + δzz)/3

(2a)

∆δ ) δzz - δiso

(2b)

η ) (δyy - δxx)/δ(0 e η e +1)

(2c)

δii ) 106 · (σref - σii)/(1 - σref) ≈ 106 · (σref - σii) (2d) asymmetry parameter (η) values. Chemical shielding tensor components, denoted as σii, can also be used to calculate these parameters, as the basic relationship relies on a 106 scaling factor (eq 2d). Note that due to this factor, the isotropic, anisotropic, and asymmetry factors are interchangeable between the chemical shift and the chemical shielding systems. These parameters are frequently used in solid-state NMR as they describe the threedimensional distribution of electron density, thus, chemical shielding, around the nucleus of interest. By measuring changes in these parameters, bond-specific data may be attained.42,43 These data show correlations in both the graphical spectra (Figure 3a) and the extracted tensor data (Table 1) for the three metal ions: magnesium, calcium, and cadmium. From these data, it is apparent that the phosphoryl centers of the teichoic acid backbone bind in a similar manner under these conditions. From the quantum mechanical simulations performed, the binding motif was found to be a direct contact-ion pairing in a bidentate manner (Figure 3b).9 In further experiments (Table 2) in which rotational speeds were varied to gain additional tensor data about cadmium-LTA binding it was found that the average chemical shift anisotropy and asymmetry parameters were 51.1 ( 0.4 ppm and 0.61 ( 0.02, respectively. The Herzfeld-Berger Analysis program provides resultant principal tensor components in such a way that standard error calculations are not viable. Therefore, we have reported errors for the CSA (∆δ) and asymmetry (η) values based on the range of results received from spectra obtained at multiple spinning speeds as performed by Aime et al.44 These data show only a small deviation present in the 3000 Hz numbers collected. This also agrees fully with the findings of Fein et al. in which EXAFS was utilized to study the binding method of cadmium with the phosphoryl sites of teichoic acid at physiological pH.4 However, the values and binding methods shown in our previous experiments were performed at high concentrations (60 and 120 mM) not usually found in nature. These studies demonstrate inner-sphere metal

336


Halye and Rice

Figure 3. (a) 31P NMR CPMAS experimental spectra from lyophilized divalent metal-bound LTA and (b) the DFT energy minimized dehydrated and hydrated molecular models of magnesium with LTA that showed the highest correlation with reduced anisotropy and asymmetry parameters extracted from the experimental spectra. Note that the experimental spectra in (a) are shown here with equal peak heights and isotropic centers. Although the isotropic chemical shift changes slightly based on the type of metal bound, this image serves to show the identical overall spectral pattern. Table 1. 31P CPMAS (3000 Hz) of LTA; Herzfeld-Berger Principal Chemical Shift Tensor Components and Associated Isotropic, Reduced Anisotropy, and Asymmetry Values for Mg2+, Ca2+, and Cd2+ Bound to LTA

σ11 σ22 σ33 σiso ∆δ η

60 mM Mg-LTA

60 mM Ca-LTA

120 mM Cd-LTA

19.8 -3.3 -41.0 -8.2 -49.3 0.70

20.3 0.2 -39.6 -6.4 -49.8 0.60

26.1 4.9 -34.9 -1.3 -50.4 0.63

chelation as determined from perturbation of the CSA tensors (Figure 3 and Table 1). At lower concentrations, such as those found in nature, metal binding does not perturb the CSA tensors. Fortunately, REDOR NMR provides the ability to characterize binding in both inner- and outer-sphere complexes. A solution of 3.8 mg of isotopically labeled cadmium-111 in 1 mL of sterile water was mixed with the lipoteichoic acid prior to REDOR experiments whose data can be used to determine the inter-

Table 2. Variable Speed 31P CPMAS of LTA; Herzfeld-Berger Principal Chemical Shift Tensor Components and Associated Reduced Anisotropy and Asymmetry Values for 120 mM CdCl2 Bound to 15 mg LTA 2.8 kHz 3.0 kHz 3.2 kHz 3.4 kHz 3.6 kHz 3.8 kHz 4.0 kHz σ11 27.9 σ22 6.3 σ33 -34.2 ∆δ -51.3 η 0.63

27.4 6.2 -33.6 -50.4 0.63

27.4 6.5 -33.9 -50.8 0.62

27.6 6.4 -34.0 -51.0 0.62

27.5 6.8 -34.3 -51.4 0.60

27.5 6.6 -34.2 -51.2 0.61

27.3 7.1 -34.4 -51.6 0.59

nuclear distance between the phosphorus core of the binding site to the chelated metal. The previous SSNMR study of binding showed that the distance from the phosphorus model compounds to the contact-ion paired metal is roughly 2.55-3.40 Å. However, the phosphoryl binding site is close enough to metals that weak dipolar interactions exist between the metal with the phosphorus atom. Thus, a 31P nucleus would experience dephasing by several 111Cd nuclei at different distances. At short dephasing times (0-6 ms), 31P signal loss is caused by the



337

Figure 4. 31P{111Cd} REDOR (10 kHz) array from 8 to 80 cycles (0.8-8.0 ms) alternating from full echo (S0) to dephased reduced echo (Sr) spectra for each dephasing time.

Figure 5. Experimentally collected phosphorus/cadmium REDOR data. Note that maximum dephasing occurs at roughly 0.75. Error bars are calculated from signal-to-noise ratios from associated spectra and standard error propagation.

primary cadmium due to its much larger dipolar coupling, whereas the secondary and tertiary cadmium atoms may not have a significant effect until dephasing times of 6-15 ms. A series of experiments were performed at dephasing times from 0.8 to 32 ms in intervals starting at 0.8 ms and increasing to 1.6 ms intervals after 16 ms. A portion of the data collected can be seen in Figure 4. Once these data were analyzed for peak heights, normalization was performed for each individual cycle count by utilizing Sr, the reduced echo, as fraction of S0, the full echo. The data, shown in Figure 5 as the normalized peak height of the reduced echo as a function of time, shows a curve fairly consistent with an initial cadmium-111 dephaser at roughly 4.5-4.75 Å. Additional consistency can be seen further down the curve for a second cadmium-111 dephaser at around 4.5-5.0 Å with a probable 10° shift from a planar orientation. Nevertheless, while these data are compelling, none of the SIMPSON simulations could account for the deviation from experimental data observed between 6 and 11 ms. To further understand this aberration from the SIMPSON predictions, some basic NMR knowledge must be applied. In standard NMR operations, the bulk signal is collected and averaged for the entire sample, giving a resultant peak (or peaks) whose intensity and integral is dependent entirely on sample concentration. However, when the REDOR pulse sequence is introduced, the Sr signal is altered only by those phosphorus-

31 nuclei that are within dipolar coupling range of the cadmium111 ions. Therefore, although the difference between the S0 and Sr peaks still holds the entirety of the dipolar coupling data, the overall data is skewed by the unavoidable inclusion of signal intensity from those phosphorus-31 nuclei that have no coordinated cadmium ions (Figure S1). However, by using the difference between S0 and Sr to find ∆S and then scaling S0 by the ratio of cadmium-coordinated phosphorus nuclei to all phosphorus nuclei into a new factor, S0′, the correction can be made. A more complete explanation of the correction procedures can be found in the Supporting Information. Corrections of this type are not uncommon in dilute systems. A previous study by this research group focused on the structure of poly(ethylene oxide) (PEO) and lithium triflate (LiCF3SO3).45,46 This study utilized 13C{7Li} REDOR and was successfully scaled due to the dilute nature of the 20:1 PEO/LiTf system. After reviewing our data and noting the maximum value of ∆S/S0 from the original plot (Figure 5), it seems that a 3:4 ratio, a scaling factor of 0.75, can be applied to correct for the ratio of phosphorus to cadmium nuclei. Initial simulations show that although a single 4.0 Å dephaser meets the initial build-up curve, it does not follow the experimental data after roughly 5 ms dephasing time (Figure 6). Additional simulations using equivalent 4.5 Å two dephaser systems show the same trend as the single dephaser data (Figure 6). Therefore, this system reveals a binding

338


Halye and Rice

Figure 6. SIMPSON REDOR (10 kHz) curve estimates after a scaling factor of 0.75 was applied to experimental data (see Figures S1 and S2 for details on scaling). Although the single dephaser 4.0 Å distance fits the initial build-up, there is considerable inconsistency after roughly 5 ms. A second dephaser simulation was performed to accommodate for this inconsistency. However, two equivalent distances (in this case, 4.5 Å to both at 0 or 180°) also fails to fully trace the path of the experimental data after 5 ms dephasing time.

Figure 7. SIMPSON REDOR (10 kHz) curve estimates after a scaling factor of 0.75 was applied to experimental data (see Figures S1 and S2 for details on scaling). The fit from the SIMPSON curves showing 111Cd coupling at roughly 4.15 and 4.90 Å shows the greatest correlation. These data reflect a much better fit than the nonscaled data. Error bars are calculated from signal-to-noise ratios from associated spectra and standard error propagation. Note that these simulations were performed with Euler angles of 0° (180°), resulting in a linear Cd-P-Cd orientation.

Figure 8. Subtle differences in the contact ion-pairing (inner sphere complex) found in high concentration metal chelation and the solventseparated ion-pairing (outer-sphere complex) found in low concentration metal chelation with teichoic acid. Note that, although the model on the right shows a possible fit for the internuclear distances measurements, there would most likely be a Coulombic repulsion between adjacent cations.

geometry in which multiple unequal dephasers interact with the phosphoryl center. Subsequent simulations reflect an initial 111Cd dephaser at roughly 4.15 Å with a second dephaser at around 4.90 Å in plane (linear Cd-P-Cd arrangement) with the first. Although Figure 7 is limited to those simulated REDOR curves that fit most closely to the experimental data points, many other

plots were calculated before making the final decision on the distance calculations. An array varying the first and second dephaser distances around the average internuclear distances measured is shown in Figure S4. Surprisingly, the 4.15 Å P-Cd distance is longer than the previous 2.5 Å distance calculated from DFT. In contrast to



339

theoretical structural model of the binding mode of cadmium to teichoic acid, and the best-fit SIMPSON input file are provided. This material is available free of charge via the Internet at http://pubs.acs.org.

References and Notes

Figure 9. Phosphodiester backbone of teichoic acid with coordinated cadmium ions (hydration shells shown as circles surrounding the cations) in a likely rotating configuration to allow for dispersal of Coulombic repulsive forces while maintaining a bridging structure of cadmium monodentate to two distinct phosphoryl centers. Note that this configuration allows for the distance and angular configuration given by current REDOR data.

the previous findings of a direct ion-pairing or inner-sphere complex47 at the high concentrations, these data support a solvent-separated ion-pairing or outer-sphere complex, in which at least one water of hydration lies between the binding site of the phosphate and the coordinated divalent cation (Figure 8). A model (Figure 9) has been developed to incorporate the REDOR internuclear distance and bond angle measurements while negating Coulombic charge repulsion down the entire length of the poly(phosphodiester) backbone. According to the model, every phosphoryl center can be rotated by roughly 90° to allow for monodentate bridging between cadmium and two phosphoryl groups. By rotating the configuration of the phosphoryl groups down the phosphodiester chain, Coulombic repulsive forces can be relieved by shielding the cations between the anionic phosphoryl centers. An alternate model can be formed by creating multiple bidentate chelation modes from phosphoryl centers to a single cadmium ion, also in an outersphere complex (Figure S3). Although this would fulfill initial distance measurements, angular and secondary dephaser distance values cannot be explained.

Conclusions These data represent a significant step forward into the understanding of the divalent metal binding mechanism as performed by Gram-positive bacteria. The previous computational modeling and SSNMR study has shown that at high metal concentrations, the phosphoryl centers of teichoic acid bind metals directly in a bidentate manner. In contrast, the current study shows that, at low metal concentrations, teichoic acid still chelates the metal cations, but in a solvent-separated ion-pairing, allowing for higher cation mobility. This arrangement is best described as two unequal monodentate P-Cd interactions (4.15 and 4.9 Å) in a linear Cd-P-Cd structure. A collection of 111 Cd{31P} REDOR experimental data should be able to elucidate the P-Cd-P structural characteristics. Whether or not the changes in metal ion concentration perturb the equilibrium constant and the rate of metal chelation remains unknown. Acknowledgment. This work is supported by the Oklahoma Center for the Advancement of Science and Technology (OCAST) and the University of Oklahoma. Special thanks to Prof. Laurel Sillerud (University of New Mexico Department of Biochemistry and Molecular Biology) for his kind donation of the >95% labeled 111CdO used in these experiments. Supporting Information Available. An explanation of REDOR scaling and error propagation procedures, an additional

(1) Ellwood, D. C. Biochem. J. 1970, 118, 367–373. (2) Ellwood, D. C.; Tempest, D. W. AdV. Microb. Physiol. 1972, 7, 83– 117. (3) Beveridge, T. J.; Doyle, R. J. Metal Ions and Bacteria; John Wiley and Sons: New York, 1989. (4) Johnson, K. J.; Cygan, R. T.; Fein, J. B. Geochim. Cosmochim. Acta 2006, 70, 5075–5088. (5) Clarke, T. E.; Vogel, H. J., Cadmium-113 and lead-207 NMR spectroscopic studies of calcium-binding proteins. Methods in Molecular Biology: Calcium-Binding Protein Protocols; Humana Press, Inc.: Totowa, NJ, 2002; Vol. 173, pp 205-215. (6) Matysik, J.; Alia; Nachtegaal, G.; van Gorkom, H. J.; Hoff, A. J.; de Groot, H. J. M. Biochemistry 2000, 39, 6751–6755. (7) McAteer, K.; Lipton, A. S.; Kennedy, M. A.; Ellis, P. D. In Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; John Wiley & Sons: Chichester, U.K., 1996; Vol. 7, pp 1085-1091. (8) Summers, M. F. Coord. Chem. ReV. 1988, 86, 43–134. (9) Wickham, J. R.; Halye, J. L.; Kashtanov, S.; Khandogin, J.; Rice, C. V. J. Phys. Chem. B 2009, 113, 2177–2183. (10) Armitage, I. M.; Boulanger, Y. Cadmium-113 NMR. In NMR of Newly Accessible Nuclei; Laszlo, P., Ed.; Academic Press: New York, 1983; Vol. 2, pp 337-365. (11) Guantieri, V.; Venzo, A.; Di Marco, V.; Acampora, M.; Biondi, B. Inorg. Chim. Acta 2007, 360, 4051–4057. (12) Rahman, M.; Patching, S. G.; Ismat, F.; Henderson, P. J. F.; Herbert, R. B.; Baldwin, S. A.; McPherson, M. J. Mol. Membr. Biol. 2008, 25, 683–690. (13) Kidambi, S.; Ramamoorthy, A. J. Phys. Chem. A 2002, 106, 10363– 10369. (14) Kidambi, S. S.; Lee, D. K.; Ramamoorthy, A. Inorg. Chem. 2003, 42, 3142–3151. (15) Kidambi, S. S.; Ramamoorthy, A. Inorg. Chem. 2003, 42, 2200–2202. (16) Srikanth, K.; Schurko, R. W.; Hung, I.; Ramamoorthy, A. Mater. Sci. Technol. 2003, 19, 1191–1196. (17) Shiman, R.; Draper, D. E. J. Mol. Biol. 2000, 302, 79–91. (18) Woodson, S. A. Curr. Opin. Chem. Biol. 2005, 9, 104–109. (19) Binder, H.; Zscho¨rnig, O. Chem. Phys. Lipids 2002, 115, 39–61. (20) Ginsburg, I. Lancet Infect. Dis. 2002, 2, 171–9. (21) Graham, L. L.; Beveridge, T. J. J. Bacteriol. 1994, 176, 1413–1421. (22) Neuhaus, F. C.; Baddiley, J. Microbiol. Mol. Biol. ReV. 2003, 67, 686– 723. (23) Peschel, A. Trends Microbiol. 2002, 10, 179–186. (24) Roethlisberger, P.; Iida-Tanaka, N.; Hollemeyer, K.; Heinzle, E.; Ishizuka, I.; Fischer, W. Eur. J. Biochem. 2000, 267, 5520–5530. (25) Stadelmaier, A.; Morath, S.; Hartung, T.; Schmidt, R. R. Angew. Chem., Int. Ed. 2003, 42, 916–920. (26) Potekhina, N. V.; Shashkov, A. S.; Evtushenko, L. I.; Senchenkova, S. y. N.; Naumova, I. B. Carbohydr. Res. 2003, 338, 2745–2749. (27) Morath, S.; Geyer, A.; Spreitzer, I.; Hermann, C.; Hartung, T. Infect. Immun. 2002, 70, 938–944. (28) Morath, S.; Stadelmaier, A.; Geyer, A.; Schmidt, R. R.; Hartung, T. J. Exp. Med. 2002, 195, 1635–1640. (29) Volkman, B. F.; Zhang, Q.; Debabov, D. V.; Rivera, E.; Kresheck, G. C.; Neuhaus, F. C. Biochem. J. 2001, 40, 7964–7972. (30) Fischer, W.; Behr, T.; Hartmann, R.; Peter-Katalinic, J.; Egge, H. Eur. J. Biochem. 1993, 215, 851–857. (31) Heaton, M. P.; Neuhaus, F. C. J. Bacteriol. 1994, 176, 681–90. (32) Behr, T.; Fischer, W.; Peterakatalinic, J.; Egge, H. Eur. J. Biochem. 1992, 207, 1063–1075. (33) Iwasaki, H.; Shimada, A.; Yokoyama, K.; Ito, E. J. Bacteriol. 1989, 171, 424–429. (34) Gross, M.; Cramton, S. E.; Gotz, F.; Peschel, A. Infect. Immun. 2001, 69, 3423–3426. (35) Baddiley, J.; Hancock, I. C.; Sherwood, P. M. A. Nature 1973, 243, 43–5. (36) Eichele, K.; Wasylishen, R. E. Herzfeld-Berger Analysis, 1.5.8; Dalhousie University and Universita¨t Tu¨bingen: Tu¨bingen, Germany, 2006. (37) Gullion, T. Concepts Magn. Reson. 1998, 10, 277–289.

340


(38) McDowell, L. M.; Schaefer, J. Curr. Opin. Struct. Biol. 1996, 6, 624– 629. (39) Schaefer, J. REDOR and TEDOR. In Encyclopedia of Nuclear Magnetic Resonance; Harris, R. K., Ed.; John Wiley: New York, 1996; pp 3983-3984. (40) Gullion, T.; Schaefer, J. J. Magn. Reson. 1989, 81, 196–200. (41) Bak, M.; Rasmussen, J. T.; Nielsen, N. C. J. Magn. Reson. 2000, 147, 296–330. (42) Alam, T. M. Ab Initio Calculations of 31P NMR Chemical Shielding Anisotropy Tensors in Phospates: The Effect of Geometry on Shielding. In Modeling NMR Chemical Shifts; Facelli, J. C., Dios, A. C. d., Eds.; American Chemical Society: Washington, DC, 1999; pp 320-334.

Halye and Rice (43) Alam, T. M. Int. J. Mol. Sci. 2002, 3, 888–906. (44) Aime, S.; Digilio, G.; Gobetto, R.; Bigi, A.; Ripamonti, A.; Roveri, N.; Gazzano, M. Inorg. Chem. 1996, 35, 149–154. (45) Wickham, J. R.; Mason, R. N.; Rice, C. V. Solid State Nucl. Magn. Reson. 2007, 31, 184–192. (46) Wickham, J. R.; York, S. S.; Rocher, N. M.; Rice, C. V. J. Phys. Chem. B 2006, 110, 4538–4541. (47) Gadd, G. M. J. Chem. Technol. Biotechnol. 2009, 84, 13–28.

BM9010479

Cadmium Chelation by Bacterial Teichoic Acid from Solid-State

Recommend Documents