Metal-induced histidine deprotonation in biocatalysis? Experimental and theoretical insights into superoxide reductase

Abstract

Metal-induced histidine deprotonation may have tremendous effects on metalloprotein catalysis. Here, we explore protonation states of all active site histidines in superoxide reductase (SOR), a non-heme iron enzyme catalysing the reduction of superoxide to hydrogen peroxide. Using experimental and theoretical techniques, we show that these amino acids remain in their neutral state under physiological conditions, excluding deprotonation. Based on our findings, alternative explanations for lack of H/D exchange of SOR histidines are discussed, including high barriers for acid/base reactions of coordinated ligands.