Roles of Amphipathicity and Hydrophobicity in the Micelle-Driven Structural Switch of a 14-mer Peptide Core from a Choline-Binding Repeat.

Choline-binding repeats (CBRs) are ubiquitous sequences with a β-hairpin core that are found in the surface proteins of several microorganisms such as S. pneumoniae (pneumococcus). Previous studies on a 14-mer CBR sequence derived from the pneumoccal LytA autolysin (LytA239-252 peptide) have demonstrated a switch behaviour for this peptide, so that it acquires a stable, native-like β-hairpin conformation in aqueous solution but is reversibly transformed into an amphipathic α-helix in the presence of detergent micelles. With the aim of understanding the factors responsible for this unusual β-hairpin to α-helix transition, and to specifically assess the role of peptide hydrophobicity and helical amphipathicity in the process, we designed a series of LytA239-252 variants affecting these two parameters and studied their interaction with dodecylphosphocholine (DPC) micelles by solution NMR, circular dichroism and fluorescence spectroscopies. Our results indicate that stabilising cross-strand interactions become essential for β-hairpin stability in the absence of optimal turn sequences. Moreover, both amphipathicity and hydrophobicity display comparable importance for helix stabilisation of CBR-derived peptides in micelles, indicating that these sequences represent a novel class of micelle/membrane-interacting peptides.