1dv6
PHOTOSYNTHETIC REACTION CENTER FROM RHODOBACTER SPHAEROIDES IN THE CHARGE-NEUTRAL DQAQB STATE WITH THE PROTON TRANSFER INHIBITOR ZN2+
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OverviewOverview
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.
About this StructureAbout this Structure
1DV6 is a Protein complex structure of sequences from Rhodobacter sphaeroides with FE2, ZN, CL, BCL, BPH, U10 and LDA as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers., Axelrod HL, Abresch EC, Paddock ML, Okamura MY, Feher G, Proc Natl Acad Sci U S A. 2000 Feb 15;97(4):1542-7. PMID:10677497
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