Coat protein conformation in M13 filaments, I-forms and spheroids

Circular dichroism studies of the filamentous coliphage M13 were carried out to determine conformational changes in the major capsid protein (the B protein) that occur during contraction of the filaments to I-forms and spheroids. The alpha-helicity of the B protein is somewhat lower in the I-forms than in filaments and much lower in spheroids. This conformational change may explain the increased detergent and lipid solubility of both I forms and spheroids relative to filaments.