TOWARDS THE UNDERSTANDING OF THE FUNCTION OF RB-SPHAEROIDES-Y WILD-TYPE REACTION CENTER - GENE CLONING, PROTEIN AND DETERGENT STRUCTURES IN THE 3-DIMENSIONAL CRYSTALS

We report various experiments aimed at the resolution of the 3-dimensional structure of the photosynthetic reaction center from wild type Y Rhodobacter sphaeroides. The genes encoding the L and M polypeptides have been cloned and sequenced. They bear 2 mutations each when compared to those already sequenced in another Rb sphaeroides strain (2.4.1). In the L gene, these codon changes are silent. In the M gene, one is silent and the other one leads to a Leu- Met substitution at position 140. At the present stage of the refinement of the X-ray data (0.3 nm resolution) the structure of the Y reaction center is shown to be highly similar to that of the Rhodopseudomonas viridis reaction center. The binding of spheroidene on the M side of the Y reaction center is shown to be determined by hydrophobic interactions with neighboring amino acids and by steric factors. Preliminary results concerning the localization of the detergent (β-octylglucoside) in the unit cell are presented. This method combines low angle neutron scattering at different contrasts in H2O/D2O with X-ray crystallographic data. © 1990.