The “chameleonic” peptide LytA239-252 forms a β-hairpin in aqueous solution which is converted into an α-helix in the presence of micelles. We have found that the balance of hydrophobicity <H> and amphipathicity <μH> contributes to helix stability.

Peptide LytA239-252 was derived from the LytA autolysin, which is involved in the infectivity of the pathogenic microorganism pneumococcus. The structural behaviour of this peptide is denoted “chameleonic” because it forms a very stable native-like β-hairpin in aqueous solution, and an also stable α-helix in the presence of detergent micelles (which have a hydrophilic surface and a hydrophobic core). Up to now it is the only reported case of a peptide whose structure switches between two ordered conformations β-hairpin to α- helix as induced by micelles. To understand the factors responsible for this unusual transition we have designed a series of peptide variants. These variants have been structurally characterised in both aqueous solution and in micelle media using NMR, circular dichroism and fluorescence. Based on these results we conclude that, when the turn sequence is not optimal, side chain interactions will be essential for β-hairpin stability, and that both hydrophobicity (<H>) and amphipathicity (<μH>) are important for helix stabilisation in the presence of micelles in a way that is not predicted by current theoretical methods. These conclusions could not only be of relevance in the field of peptide design and biosensors, but may also help to understand the molecular basis for the peculiar mechanism of LytA translocation from the cytoplasm to the bacterial surface.

These results have just been published in:

Zamora-Carreras, H., Maestro, B., Strandberg, E., Ulrich, A.S., Sanz, J.M., Jiménez, M.A.. Roles of amphipathicity and hydrophobicity in the micelle-driven structural switch of a 14-mer peptide core from a choline-binding repeat. Chem. Eur J. 24, 5825-5839 (2018). doi: 10.1002/chem.201704802

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