Laser raman studies of lipid disordering by the B-protein of fd phage

Complexes of the B-protein of fd phage with the model lipid dipalmitoyl phosphatidylcholine (DPPC) were made by sonication of the fd phage in the presence of dipalmitoyl phosphatidylcholine. Both laser Raman spectra and circular dichroism show the protein in the membrane to be almost entirely in the β-sheet conformation. This β-sheet conformation is found to be independent of the temperature between 10° C and 50° C. On the other hand, the protein has a very dramatic effect on the organization of the lipid bilayer. An aqueous dispersion of 1 : 1 lipid/protein mixture gives a broad conformational transition of DPPC which occurs between 10° C and 30° C. This contrasts markedly with simple aqueous DPPC dispersions which show a sharp transition at 41°C. This appears to be the first reported example of the lowering of the conformational transition of a membrane bilayer by an intrinsic membrane protein.