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.USA 97: 1542-1547
- PubMed: 10677497
- Primary Citation of Related Structures:
- PubMed Abstract:
- 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
- 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.USA 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
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 re ...
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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