STRUCTURAL MODEL OF THE PHOTOSYNTHETIC REACTION-CENTER OF RHODOBACTER-CAPSULATUS

The reaction center (RC) from the photosynthetic bacterium Rhodobacter (Rb.) capsulatus has been the subject of a considerable amount of mol ecular biological and spectroscopic work aimed at improving our unders tanding of the primary steps of photosynthesis. However, no three-dime nsional structure is available for this protein. We present here a mod el obtained by combining information from the structure of the highly homologous RC from Rhodopseudomonas (Rps.) viridis with molecular mech anics and simulated annealing calculations. In the Rb. capsulatus mode l the orientations of the bacteriochlorophyll monomer and the bacterio pheophytin on the branch inactive in electron transfer differ signific antly from those in the RCs of Rps. viridis and Rb. sphaeroides. The b acteriopheophytin orientational difference is in good accord with prev ious linear dichroism measurements. A comparison is made of interactio ns between the pigments and the protein environment that may be of fun ctional significance in Rps. viridis, Rb. sphaeroides, and Rb, capsula tus. (C) 1995 Wiley-Liss, Inc.