Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers.Axelrod, H.L., Abresch, E.C., Paddock, M.L., Okamura, M.Y., Feher, G.
(2000) Proc Natl Acad Sci U S A 97: 1542-1547
- PubMed: 10677497
- DOI: 10.1073/pnas.97.4.1542
- Primary Citation of Related Structures:
1DS8, 1DV3, 1DV6
- PubMed Abstract:
- Identification of the Proton Pathway in Bacterial Reaction Centers: Inhibition of Proton Transfer by Binding of Zn2+ or Cd2+
Paddock, M.L., Graige, M.S., Feher, G., Okamura, M.Y.
(1999) Proc Natl Acad Sci U S A 96: 6183
- Identification of proton transfer pathways in the X-ray crystal structure of the bacterial reaction center from Rhodobacter sphaeroides
Abresch, E.C., Paddock, M.L., Stowell, M.H.B., McPhillips, T.M., Axelrod, H.L., Soltis, S.M., Rees, D.C., Okamura, M.Y., Feher, G.
(1998) Photosynth Res 55: 119
- Light-Induced Structural Changes in Photosynthetic Reaction Center: Implications for Mechanism of Electron-Proton Transfer
Stowell, M.H., McPhillips, T.M., Rees, D.C., Soltis, S.M., Abresch, E., Feher, G.
(1997) Science 276: 812
The reaction center (RC) from Rhodobacter sphaeroides couples light-driven electron transfer to protonation of a bound quinone acceptor molecule, Q(B), within the RC. The binding of Cd(2+) or Zn(2+) has been previously shown to inhibit the rate of reduction and protonation of Q(B) ...
The reaction center (RC) from Rhodobacter sphaeroides couples light-driven electron transfer to protonation of a bound quinone acceptor molecule, Q(B), within the RC. The binding of Cd(2+) or Zn(2+) has been previously shown to inhibit the rate of reduction and protonation of Q(B). We report here on the metal binding site, determined by x-ray diffraction at 2.5-A resolution, obtained from RC crystals that were soaked in the presence of the metal. The structures were refined to R factors of 23% and 24% for the Cd(2+) and Zn(2+) complexes, respectively. Both metals bind to the same location, coordinating to Asp-H124, His-H126, and His-H128. The rate of electron transfer from Q(A)(-) to Q(B) was measured in the Cd(2+)-soaked crystal and found to be the same as in solution in the presence of Cd(2+). In addition to the changes in the kinetics, a structural effect of Cd(2+) on Glu-H173 was observed. This residue was well resolved in the x-ray structure-i.e., ordered-with Cd(2+) bound to the RC, in contrast to its disordered state in the absence of Cd(2+), which suggests that the mobility of Glu-H173 plays an important role in the rate of reduction of Q(B). The position of the Cd(2+) and Zn(2+) localizes the proton entry into the RC near Asp-H124, His-H126, and His-H128. Based on the location of the metal, likely pathways of proton transfer from the aqueous surface to Q(B) are proposed.
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