PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

Towards Structural determination of the Rhodobacter sphaeroides core-LHI antenna. Eva Pebay-Peyroula¹, Dominique Cannella¹, Colette Jungas^*,2, ¹ Institut de Biologie Structurale, Grenoble, France²

ABSTRACT- In photosynthetic membranes of the purple bacteria, the RC and LH1 antenna form stoichiometric complex called the RC-LH1 core complex. In Rhodobacter sphaeroides and Rhodobacter capsulatus, anaerobic photosynthetic growth requires the presence of an additional PufX polypeptide. Apparently, this polypeptide is only required when the LH1 antenna complex is present and intact. In a previous study, we reported the structure of the core-LH1 antenna in native tubular membranes of LH2-deleted Rb. sphaeroides strain. The projection map revealed two "C"-shaped incomplete antenna rings each surrounding one RC. All the experimental results are consistent with the idea that PufX facilitates, either directly or indirectly the exchange of quinones between the RC site and the cyt bc1 complex. In order to understand the role of PufX, a core complex preparation from Rb sphaeroides, which is suitable for three-dimentional crystallization, was developped. The nonionic detergent dodecyl maltoside was selected for solubilisation on the basis of efficiency to extract the core-LH1 complex in a fully active dimeric state from the photosynthetic membranes. The RC-LH1-PufX complex was purified by a continuous sucrose density gradient followed by an anion exchange chromatography using a monoQ column (Amersham). This preparation represents a available material for three-dimensional crystallization trials of the core-LH1 complex Crystals were obtained with the protein purified. Those crystals grown in dodecylmaltoside diffracted X-rays to 17 . Ways to further improve the crystal quality are discussed.

KEY WORDS: reaction center, purple bacteria