title: Structure of the detergent phase and protein-detergent interactions in crystals of the wild-type (strain Y) Rhodobacter sphaeroides photochemical reaction center.
abstract: Rhodobacter sphaeroides (strain Y) reaction center (RC) crystals were grown in the presence of n-octyl beta-glucoside (beta-OG). In order to determine the structure of the detergent phase in these crystals, low-resolution neutron diffraction experiments were performed at different contrasts obtained by varying the H2O/D2O ratio in the solvent. From the contrast variation data and from the RC atomic coordinates determined by X-ray diffraction [Arnoux, B., Ducruix, A., Reiss-Husson, F., Lutz, M., Norris, J., Schiffer, M., & Chang, C. H. (1989) FEBS Lett. 258, 47-50], a model was obtained for the structure of the detergent phase in the crystal. The detergent forms a ring-shaped micelle surrounding the most hydrophobic part of the transmembrane alpha helices of the RC. Each detergent ring is connected to two next-neighbor rings by intermicellar bridges. The detergent phase is organized thus in infinite zigzag chains parallel to the b axis of the P2(1)2(1)2(1) unit cell. The main interactions between beta-OG molecules and the RC molecules are hydrophobic and are localized at the level of the transmembrane alpha helices. This interaction replaces the phospholipid-protein interaction existing in vivo in the membrane and, to some extent, also the light harvesting complex-protein interaction. Secondary hydrophilic interactions are found between a few of the charged residues of the H subunit and the hydrophilic surface of the detergent ring from a neighboring RC molecule. A comparison with a previous study on Rhodopseudomonas viridis crystals [which grow in the presence of lauryldimethylamine N-oxide (LDAO) and belong to a different space group] [Roth, M., Lewit-Bentley, A., Michel, H., Deisenhofer, J., Huber, R., & Oesterhelt, D. (1989) Nature 340, 659-661] shows a quasi identity of shape and position of the beta-OG and LDAO rings around the transmembrane alpha helices. The secondary interactions, involving in both cases the external surface of the H subunit, differ because of the different molecular packing in the two space groups. The role and structural requirements of the detergent in the crystallization process are discussed.
authors.affiliation: Laboratoire d'Ingénierie des Protéines, LIP/LCCP, Centre d'Etudes Nucléaires de Grenoble, France.
authors.forename: M
authors.initials: M
authors.lastname: Roth
authors.forename: B
authors.initials: B
authors.lastname: Arnoux
authors.forename: A
authors.initials: A
authors.lastname: Ducruix
authors.forename: F
authors.initials: F
authors.lastname: Reiss-Husson
mesh_terms: D000465:Algorithms; D003196:Computer Graphics; D003461:Crystallography; D003902:Detergents / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry*; D008958:Models, Molecular; D009502:Neutrons; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D012242:Rhodobacter sphaeroides / Q000032:analysis*; D012542:Scattering, Radiation; D013045:Species Specificity
chemical_list: D003902:Detergents; D005960:Glucosides; D045322:Photosynthetic Reaction Center Complex Proteins; C018619:octyl-beta-D-glucoside