Analysis of peptaibol sequence composition: implications for in vivo synthesis and channel formation.

The sequence entries in the Peptaibol Database were analysed to provide information on compositional features of this unusual family of peptides. The non-standard amino acid alpha-aminoisobutyric acid represents almost 40% of the residues in all the known sequences. Glutamine is the only significant polar residue in peptaibols, and the position and number of these residues appear to be related to their functional properties as ion channels. Aromatic residues are clustered at the termini, which may contribute to stabilization of the peptide vertically within the bilayer. The peptide chain length is strongly weighted towards the longer members of the family (16-20 residues) and likely to be an important feature in their mode of action as transmembrane permeabilizers. The significant skewing towards even numbers of residues and the bias in pairwise distributions of amino acids have implications for the nature of the in vivo synthesis of these peptides via large non-ribosomal protein complexes.