Micelle-Triggered b-Hairpin to a-Helix Transition in a 14-Residue Peptide from aBinding Choline- Repeat of the Pneumococcal Autolysin LytA

Abstract

Choline-binding modules (CBMs) have a bb-solenoid structure composed of choline-binding repeats (CBR), which consist of a b-hairpin followed by a short linker. To find minimal peptides that are able to maintain the CBR native structure and to evaluate their remaining cholinebinding ability, we have analysed the third b-hairpin of the CBM from the pneumococcal LytA autolysin. Circular dichroism and NMR data reveal that this peptide forms a highly stable native-like b-hairpin both in aqueous solution and in the presence of trifluoroethanol, but, strikingly, the peptide structure is a stable amphipathic a-helix in both zwitterionic (dodecylphosphocholine) and anionic (sodium dodecylsulfate) detergent micelles, as well as in small unilamellar vesicles. This b-hairpin to a-helix conversion is reversible. Given that the b-hairpin and a-helix differ greatly in the distribution of hydrophobic and hydrophilic side chains, we propose that the amphipathicity is a requirement for a peptide structure to interact and to be stable in micelles or lipid vesicles. To our knowledge, this “chameleonic” behaviour is the only described case of a micelle-induced structural transition between two ordered peptide structures.