Photosynthetic Reaction Centers of Purple Bacteria

A Comparison of Stigmatellin Conformations, Free and Bound to the Photosynthetic Reaction Center and the Cytochrome bc1 Complex

“…The Q B site is formed primarily by residues located on transmembrane helices D (L171-L198) and E (L226-L249) as well as on the intervening cytoplasmic de helix (L209-L220) and the dee loop (L220-L226). 21,22 In addition, the Q B site is delimited against the membrane by the atoms of two cofactors, the phytyl Figure 1. Stigmatellin-binding sites in the cytochrome bc 1 complex (left) and the photosynthetic RC (right).…”

Substitution of isoleucine L177 by histidine in Rhodobacter sphaeroides reaction center results in the covalent binding of PA bacteriochlorophyll to the L subunit

“…According to the current knowledge, the mutual distances and orientations of the pigments are specifically controlled by the surrounding protein [2]. For the last decades a good deal of data on protein‐cofactor interactions in photosynthetic RCs was accumulated by means of site‐directed mutagenesis [3].…”

Ubiquinone (coenzyme Q10) binding sites: Low dielectric constant of the gate prevents the escape of the semiquinone

“…Several different positions of neutral Q B have been found in RC crystal structures [42][43][44][45][46][47][48][49]. Time-resolved crystallographic experiments indicate predominant binding of Q B in the proximal position in both the neutral and charge-separated states and no large motion associated with Q B was observed after the flash on the timescale of secondary electron transfer [50,51].…”

“…The location of quinones in quinone-binding proteins, including bacterial RCs [44], Photosystem I [62], Photosystem II [63], and bc 1 complex [64], has been determined in many crystal structures. In all known structures, the quinone headgroup is oriented towards the membrane surface, while the tail is exposed to the membrane dielectric (Fig.…”

“…Hydrogen bonds play important roles for binding and stabilization of neutral and semiquinone forms of Q B . Many putative hydrogen‐bonding partner(s) to Q B and have been identified in different RC crystal structures [42–49].…”