Formation of non-bilayer structures induced by M13 coat protein depends on the conformation of the protein

Abstract

A comparison is made of the interaction of the coat protein of bacteriophage M13 in a predominant α-helix conformation and in a predominant β-sheet conformation. To perform a systematic study of the interaction between the protein in these two different forms and the surrounding lipid matrix. NMR spectra of 2H-nuclei of specific labelled phospholipid systems are measured. In addition 31P-NMR is employed to provide information about the morphological structure adopted by the reconstituted lipid/protein systems. From the 2H-NMR studies on specific headgroup and chain deuterium labelled phospholipids it is found that the protein in the predominant β-sheet conformation causes of fraction of lipids to be trapped. By combining the results from the headgroup and acyl chains of the phospholipids, it is concluded that the trapped lipids are arranged in a non-bilayer structure, probably caused by a misfitting of the hydrophobic core of the protein and the membrane bilayer. The protein in the predominant α-helix conformation perfectly fits in the lipid bilayer and has only minor influences on the surrounding lipid matrix. A new model is proposed to explain the presence of the trapped lipids in the lipid/protein systems.