Interaction between cytochrome c2 and the photosynthetic reaction center from Rhodobacter sphaeroides: effects of charge-modifying mutations on binding and electron transfer.

The electrostatic interactions governing binding and electron transfer from cytochrome c(2) (cyt c(2)) to the reaction center (RC) from the photosynthetic bacteria Rhodobacter sphaeroides were studied by using site-directed mutagenesis to change the charges of residues on the RC surface. Charge-reversing mutations (acid --> Lys) decreased the binding affinity for cyt c(2). Dissociation constants, K(D) (0.

Co-crystallization and characterization of the photosynthetic reaction center-cytochrome c2 complex from Rhodobacter sphaeroides.

The photosynthetic reaction center (RC) of Rhodobacter sphaeroides and cytochrome c2 (cyt c2), its physiological secondary electron donor, have been co-crystallized. The molar ratio of RC/cyt c2 was found by SDS-PAGE and optical absorbance changes in the co-crystals to be 4. The crystals diffracted X-rays to 3.

Pathway of proton transfer in bacterial reaction centers: role of aspartate-L213 in proton transfers associated with reduction of quinoneto dihydroquinone.

The role of Asp-L213 in proton transfer to reduced quinone QB in the reaction center (RC) from Rhodobacter sphaeroides was studied by site-directed replacement of Asp with residues having different proton donor properties. Reaction centers (RCs) with Asn, Leu, Thr, and Ser at L213 had greatly reduced (approximately 6000-fold) proton-coupled electron transfer [kAB(2)] and proton uptake rates associated with the second electron reduction of QB (QA- QB- + 2H(+)-->QAQBH2) compared to native RCs. RCs containing Glu at L213 showed faster (approximately 90-fold) electron and proton transfer rates than the other mutant RCs but were still reduced (approximately 70-fold) compared with native RCs.

Pathway of proton transfer in bacterial reaction centers: second-site mutation Asn-M44-->Asp restores electron and proton transfer in reaction centers from the photosynthetically deficient Asp-L213-->Asn mutant of Rhodobacter sphaeroides.

Site-directed mutagenesis of the photosynthetic reaction center (RC) from Rhodobacter sphaeroides has shown Asp-213 of the L subunit (Asp-L213) to be important for photosynthetic viability. Replacement of Asp-L213 with Asn resulted in a photosynthetically deficient mutant, due to the 10(4)-fold slower rate for the proton-coupled electron transfer reaction QA-QB- + 2H+-->QAQBH2 (k(2)AB). The detrimental effect of Asn-L213 is surprising since RCs from Rhodopseudomonas viridis, Rhodospirillum rubrum, and Chloroflexus aurantiacus have Asn at the homologous position.

Pathway of proton transfer in bacterial reaction centers: replacement of glutamic acid 212 in the L subunit by glutamine inhibits quinone (secondary acceptor) turnover.

The mechanism of proton transfer in the reaction centers (RCs) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Replacement of Glu-212 of the L subunit, a protonatable residue located near the secondary acceptor (QB) binding site, by glutamine reduced the in vitro electron turnover from cytochrome c to 2,3-dimethoxy-5-methylbenzoquinone (UQ0) by a factor of 25. The electron transfer rate to QB remained essentially unimpaired.

Reaction centers from three herbicide-resistant mutants of Rhodobacter sphaeroides 2.4.1: sequence analysis and preliminary characterization.

Many herbicides that inhibit photosynthesis in plants also inhibit photosynthesis in bacteria. We have isolated three mutants of the photosynthetic bacterium Rhodobacter sphaeroides that were selected for increased resistance to the herbicide terbutryne. All three mutants also showed increased resistance to the known electron transfer inhibitor o-phenanthroline.