Structure of membrane-embedded M13 major coat protein is insensitive to hydrophobic stress

¹ Laboratory of Biophysics, Wageningen University

^* To whom correspondence should be addressed. E-mail: marcus.hemminga{at}wur.nl.

Submitted on May 14, 2007
Revised on June 19, 2007
Accepted on 26 July 2007

	Abstract

The structure of a membrane-embedded -helical reference protein, the M13 major coat protein, is characterized under different conditions of hydrophobic mismatch using Fluorescence Resonance Energy Transfer (FRET) in combination with high-throughput mutagenesis. We show that the structure is similar in both thin 14:1 and in thick 20:1 phospholipid bilayers, indicating that the protein does not undergo large structural rearrangements in response to conditions of hydrophobic mismatch. We introduce a "helical fingerprint" analysis, showing that in both phospholipid bilayers the amino acid residues 1-9 are unstructured. Our findings indicate the presence of -helical domains in the transmembrane segment of the protein, however, no evidence is found for a structural adaptation to the degree of hydrophobic mismatch. In the light of the present literature and based on our data, we conclude that aggregation (at high protein concentration) and adjustment of the tilt angle and of the lipid structure are the dominating responses to conditions of hydrophobic mismatch.

Key Words: FRET constraints, fluorescence spectroscopy, hydrophobic mismatch, membrane protein conformation, site-directed labeling

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