Asymmetric alpha-helicity loss within a peptide adsorbed onto charged colloidal substrates

A combination of circular dichroism and solution 1H NMR spectroscopy provides a localized description of the distribution of alpha -helical structure within the capped peptide DDDDAAAAARRRR (4DAR5) in aqueous solution and adsorbed onto anionic and cationic colloidal substrates. The adsorption-induced conformational changes are different from those observed upon heating 4DAR5 in solution, in which case the alanine segment remains largely alpha -helical and the transition to a coil structure propagates from the termini. Adsorption is driven by electrostatic complementarity, which places the charged peptide segment adjacent to the substrate of opposite charge. A similar pattern of alpha -helicity loss is observed whether the peptide is adsorbed onto anionic or cationic colloidal silica, despite inverse orientations; significant alpha -helicity loss occurs within the central alanine segment and the terminal arginine segment, whereas alpha -helicity is retained in the aspartate segment. This pattern of adsorption-induced conformational change illustrates the complex and subtle balance among the intramolecular and intermolecular factors that influence the conformations of adsorbed peptides and proteins.