Self diffusion and spectral modifications of a membrane protein, the Rubrivivax gelatinosus LH2 complex, incorporated into a monoolein cubic phase

The light-harvesting complex LH2 from a purple bacterium, Rubrivivax gelati nosus, has been incorporated into the Q230 cubic phase of monoolein. We mea sured the self-diffusion of LH2 in detergent solution and in the cubic phas e by fluorescence recovery after photobleaching. We investigated also the a bsorption and fluorescence properties of this oligomeric membrane protein i n the cubic phase, in comparison with its P-octyl glucoside solution. In th ese experiments, native LH2 and LH2 labeled by a fluorescent marker were us ed. The results indicate that the inclusion of LH2 into the cubic phase ind uced modifications in the carotenoid and B800 binding sites. Despite these significant perturbations, the protein seems to keep an oligomeric structur e. The relevance of these observations for the possible crystallization of this protein in the cubic phase is discussed.