Conformation and orientation of the gene 9 minor coat protein of bacteriophage M13 in phospholipid bilayers

The membrane-bound state of the gene 9 minor coat protein of bacteriophage M13 was studied in model membrane systems, which varied in lipid head group and lipid acyl chain composition. By using FTIR spectroscopy and subsequen t band analysis a quantitative analysis of the secondary structure of the p rotein was obtained. The secondary structure of the gene 9 protein predomin antly consists of alpha -helical (67%) and turn (33%) structures. The turn structure is likely to be located C-terminally where it has a function in r ecognizing the phage DNA during bacteriophage assembly. Attenuated total re flection FTIR spectroscopy was used to determine the orientation of gene 9 protein in the membrane, revealing that the alpha -helical domain is mainly transmembrane. The conformational and orientational measurements result in two models for the gene 9 protein in the membrane: a single transmembrane helix model and a two-helix model consisting of a 15 amino acid long transm embrane helix and a 10 amino acid long helix oriented parallel to the membr ane plane. Potential structural consequences for both models are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.