Interactions between Charged Polypeptides and Non-Ionic Surfactants

¹ Lund University
² AstraZeneca R&D Lund

^* To whom correspondence should be addressed. E-mail: stefan.ulvenlund{at}astrazeneca.com.

Submitted on April 26, 2005
Revised on June 1, 2005
Accepted on 29 August 2005

	Abstract

The influence of molecular characteristics on the mutual interaction between peptides and non-ionic surfactants has been investigated by studying the effects of surfactants on amphiphilic, random co-polymers of -L-amino acids, containing lysine residues as the hydrophilic parts. The hydrophobic residues were either phenylalanine or tyrosine. The peptide-surfactant interactions were studied by means of circular dichroism (CD) spectroscopy and binding isotherms, as well as by 1D and 2D NMR. The binding of surfactant to the peptides was found to be a cooperative process, appearing at surfactant concentrations just below the critical micellar concentration (CMC). However, a certain degree of peptide hydrophobicity is necessary to obtain an interaction with non-ionic surfactant. When this prerequisite is fulfilled, the peptide mainly interacts with self-assembled, micelle-like surfactant aggregates formed onto the peptide chain. Therefore, the peptide-surfactant complex is best be described in terms of a necklace model, with the peptide interacting primarily with the palisade region of the micelles via its hydrophobic sidechains. The interaction yields an increased amount of -helix conformation in the peptide. Surfactants that combine small headgroups with a propensity to form small, nearly spherical micelles were shown to give the largest increase in -helix content.

Key Words: CD spectroscopy, NMR spectroscopy, alkylglycoside, alpha-helix stabilization, binding isotherm, polyamino acids