Reversible electrochemical triggering of the random coil to α-helix conformational transition of polylysine, and secondary folding of reflectin A1, was accomplished at a Pt electrode at potentials < |1| V vs. Ag/AgCl. Direct electroreduction of the N-terminus vs. ε-amino groups in lysine (Lys) sidechains, imidazolium groups of histidine-containing reflectin A1, 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, circular dichroism, and dynamic light scattering to dynamically follow the evolution of secondary folding and assembly of polylysine and reflectin 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 in polylysine. The site-selective electrochemistry and optical methodologies to be 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.

[1] E. Masquelier, S.P. Liang, L. Sepunaru, D. E. Morse, M. J. Gordon, "Reversible Electrochemical Triggering and Optical Interrogation of Polylysine α-helix formation " Bioelectrochemistry vol. 144, p. 108007, 04/2020 2022, doi: 10.1016/j.bioelechem.2021.108007

[2] S. P. Liang, R. Levenson, B. Malady, M. J. Gordon, D. E. Morse, and L. Sepunaru, "Electrochemistry as a surrogate for protein phosphorylation: voltage-controlled assembly of reflectin A1," J R Soc Interface, vol. 17, no. 173, Dec 23 2020, doi: 10.1098/rsif.2020.0774.