Coupling to Lysine-13 Promotes Electron Tunneling through Carboxylate-Terminated Alkanethiol Self-Assembled Monolayers to Cytochrome <i>c</i>

Abstract

Electrochemistry of surface-modified cytochrome c (cyt c) bound electrostatically to carboxylate-terminated alkanethiol self-assembled monolayers (SAM) reveals highly anisotropic electronic coupling across the protein/monolayer interface. Substitution of a lysine residue with alanine at position 13 in recombinant rat cyt c (RC9-K13A) lowers the interfacial electron transfer (ET) rate more than 5 orders of magnitude, whereas ET is only slightly affected by replacement of lysine-72 or lysine-79 with alanine. The results clearly show that lysine-13 is directly involved in coupling the protein to the SAM carboxylate terminus. Interfacial ET rates for both yeast iso-1 cyt c and the mutant RC9-K13R indicate that arginine-13 couples the protein to the carboxylate interface less well than lysine-13.