Roles of amphipathicity and hydrophobicity in the micelle-driven structural switch of a 14-mer peptide core from a choline-binding repeat

Abstract

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.