Transmembrane Segment Peptides of the Ff Phage Major Coat Protein Form Parallel Homodimers

Abstract

The Ff filamentous phage major coat protein (MCP) is located in the inner membrane of host cell Escherichia coli prior to assembly into the lipid-free virion. The 50-residue MCP consists of a mobile N-terminal amphipathic helix that is connected by a helical hinge region to a ca 20-residue transmembrane helix. In membrane environments the MCP has been shown to specifically self-associate into dimers in both in vitro [1] and in vivo [2] studies. In the present work, peptide versions of the MCP lacking the N-terminal arm were synthesized with the sequence KKKC-Y₂₁IGYA-WAMVVVIVGATIGIKLFKKFTSK₄₈-amide in order to investigate the orientation of the MCP transmembrane domains in detergent micelles. Peptides were labeled with pyrene fluorophores at the N-terminal Cys residue to establish the topology (ie. parallel vs anti-parallel) of the homodimers in detergent micelles using excimer fluorescence experiments. Experiments were carried out in two detergents, sodium dodecyl sulfate (SDS) and perfluorooctanoate (PFO) to investigate whether there was any correlation between the degree of excimer fluorescence and type of membrane mimetic environment used.