Orientation and assignment of the four cytochrome hemes in Rhodopseudomonas viridis reaction centers

Abstract

Low temperature absorption and linear dichroism measurements on oriented reaction centers of Rhodopseudomonas viridis at different redox potentials allow the ~t-bands of the four heroes to be spectrally resolved. The high-potential heine C556 presents an ~t-band split into two components absorbing at 555 and 551 nm. The corresponding linear dichroism spectrum shows two transitions of opposite sign and equal amplitudes. Comparison of our experimental results with the linear dichroism values calculated from the atomic coordinates leads us to assign unambiguously the high-potential C55 ~ cytochrome with heine 2, the third heme away from the primary donor. Taken together with other available spectroscopic observations, this result implies the following sequence for the redox centers in Rhodopseudomonas viridis: C554 C556 C552 C55~ P.

Electrostatic Interaction between Redox Cofactors in Photosynthetic Reaction Centers

“…As a consequence, the electrostatic interaction between these two redox centers contributes to upshift the apparent E m of P when compared with the native VC-F RC. In B. viridis, the resolution of the threedimensional structure (9) and the determination of the order of the hemes in the cytochrome subunit (24,27,28) grounded several studies that emphasized the role of intercofactor electrostatic interaction. Based on the finding that the oxidation of the outermost solvent-exposed hemes was moderately electrogenic, Gao agreement with our finding.…”

Shortcut of the photosynthetic electron transfer in a mutant lacking the reaction center‐bound cytochrome subunit by gene disruption in a purple bacterium, Rubrivivax gelatinosus

“…The electron transfer function and characterization of hemes in the cytochrome subunit has been widely studied in various purple bacteria (e.g, R. viridis [2][3][4][5][6][7][8][9][10][11][12], Rhodospirillum molischianum [13], Rubrivivax gelatinosus [14][15][16], Rhodof erax fermentans [17], Chromatium vinosum [18], and Rhodopseudomonas acidophila [19]). These studies have presented that the four hemes in the cytochrome subunit differ in redox midpoint potentials (Em) and peak wavelengths of the a-absorption bands, as shown in a recent review by Nitschke and Dracheva *Corresponding author.…”

Two Distinct Binding Sites for High Potential Iron-Sulfur Protein and Cytochrome c on the Reaction Center-bound Cytochrome of Rubrivivax gelatinosus

“…We selected the reduced form of c 551 (Protein Data Bank code 451C (34)) to build the structural framework because it possesses the highest resolution (1.6 Å) and best R-factor (0.187) among all the c 551 crystal structures in Protein Data Bank. According to multiple sequence alignments, residue Gly 39 in the template (451C) was deleted, and three residues were inserted at position 63 for cytochrome c 8 . Since the insertion region is near the heme and a conserved helix, we tilted the C-terminal helix to shift its N terminus away from the heme by about 2.6 Å such that there is enough space to accommodate the three inserted residues.…”

“…Third, armed with mutagenesis data (19), we developed a set of restrained distances between the side chain atoms of cytochrome c 8 and the RC-bound cytochrome. More explicitly, the distance restraint for atom CBC of heme 4(I) and that of the cytochrome c 8 3 A rigid body energy minimization was performed by using the X-PLOR nuclear Overhauser effect statement to incorporate the distance restraints. We assigned the averaged interatomic distance to the center of a square-well potential function used in minimization.…”

“…The four hemes are arranged linearly and labeled as starting from P, heme 1(III), heme 2(IV), heme 3(II), and heme 4(I). The spatial arrangement of the four hemes presents a high-low-high-low sequence in terms of redox potential 2 (1,8,9). Two types of soluble electron carrier proteins have been shown to act as the electron donors to the RC-bound cytochrome.…”