Oblique orientated α-helices possess hydrophobicity gradients, which allow the parent α-helices to penetrate the membrane at a shallow angle, thereby destabilising membrane lipid organisation and promoting a range of biological processes. These α-helices occur in a variety of membrane interactive proteins and a number of techniques have been developed to guide their identification using sequence data alone. Hydrophobicity profiling, which provides a onedimensional analysis of sequence data, identified only 30% of known tilted peptides in a control dataset and was thus of limited predictive use. In contrast, extended hydrophobic moment plot methodology and amphipilic profiling which take residue distribution into account and provide two-dimensional analysis of primary structural data, were found to be good indicators of tilted peptide structure. Amphiphilic profiling identified 67% of tilted peptides in the control dataset and showed that potentially, approximately 40% of transmembrane a-helices possess tilted peptide structure. However, it has been shown that extending these simple methods to take into account the three-dimensional spatial distribution of residues gives no clear additional benefit to identifying tilted peptides.
Keywords: Oblique orientated α-helix, hydrophobic moment, hydrophobicity profiling, amphiphilicity profiling, transmembrane protein
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