Peptide mimics of the M13 coat protein transmembrane segment - Retention of helix-helix interaction motifs

Sequence-specific noncovalent helix-helix interactions between transmembran e (TM) segments in proteins are investigated by incorporating selected TM s equences into synthetic peptides using the construct CKKK-TM-KKK. The pepti des are of suitable hydrophobicity for spontaneous membrane insertion, wher eas formation of an N-terminal S-S bond can bring pairs of TM helices into proximity and promote their parallel orientation. Using the propensity of t he protein to undergo thermally induced alpha-helix --> beta-sheet transiti ons as a parameter for helix stability, we compared the wild type and mutan t (V29A and V31A) bacteriophage M13 coat proteins with their corresponding TM peptide constructs (M13 residues 24-42). Our results demonstrated that t he relevant helix-helix tertiary contacts found in the intact proteins pers ist in the peptide mimics. Molecular dynamics simulations support the tight "two in-two out" dimerization motif for V31A consistent with mutagenesis d ata. The overall results reinforce the notion of TM segments as autonomous folding domains and suggest that the generic peptide construct provides a v iable reductionist system for membrane protein structural and computational analysis.