Reversible electrochemical triggering and optical interrogation of polylysine α-helix formation

Abstract

Reversible electrochemical triggering of the random coil to α-helix conformational transition of polylysine (Lys₁₀, Lys₂₀, Lys₅₀) was accomplished at a Pt electrode at potentials < |1| V vs. Ag/AgCl. Direct electroreduction of the N-terminus vs ε-amino groups in Lys sidechains, as well as hydronium reduction and electrolysis, could be easily distinguished and deconvolved using differential pulse voltammetry. Electrochemistry was coupled with in situ UV absorbance and circular dichroism spectroscopies to dynamically follow the evolution of α-helix formation at different potentials. Isotope experiments in H₂O vs. D₂O unequivocally confirm that direct electroreduction of ε-NH₃⁺/ND₃⁺ groups in Lys sidechains, rather than electrochemically generated pH gradient-induced deprotonation, leads to subsequent α-helix formation. The site-selective electrochemistry and optical methodologies presented herein can be generalized and extended to interrogate other protonation-sensitive biomolecular systems, and potentially provide access to early intermediates and control over the dynamic structural evolution of peptides and proteins.

Keywords: Alpha-helix; Circular dichroism; Coil-to-helix transition; Electroreduction; Polylysine.