Induced conformational changes upon Cd2+ binding at photosynthetic reaction centers.

ABSTRACT: Cd(2+) binding at the bacterial photosynthetic reaction center (bRC) from Rhodobacter sphaeroides is known to inhibit proton transfer (PT) from bulk solvent to the secondary quinone Q(B). To elucidate this mechanism, we calculated the pK(a) for residues along the water channels connecting Q(B) with the stromal side based on the crystal structures of WT-bRC and Cd(2+)-bound bRC. Upon Cd(2+) binding, we observed the release of two protons from His-H126/128 at the Cd(2+) binding site and significant pK(a) shifts for residues along the PT pathways. Remarkably, Asp-L213 near Q(B), which is proposed to play a significant role in PT, resulted in a decrease in pK(a) upon Cd(2+) binding. The direct electrostatic influence of the Cd(2+)-positive charge on these pK(a) shifts was small. Instead, confo

SUBMITTER: Ishikita H 

PROVIDER: S-EPMC1283420 | biostudies-literature | 2005 Nov

REPOSITORIES: biostudies-literature