The functional roles of the three copper sites associated with the methionine-rich insert in the multicopper oxidase CueO from E. coli

Abstract

CueO from Escherichia coli is a multicopper oxidase (MCO) involved in copper tolerance under aerobic conditions. It features the four typical copper atoms that act as electron transfer (T1) and dioxygen reduction (T2, T3; trinuclear) sites. In addition, it displays a methionine- and histidine-rich insert that includes a helix that blocks physical access to the T1 site. In crystalline form, the insert provides at least three additional Met-rich Cu(i) binding sites Cu5 (sCu), Cu6 and Cu7 that are proposed to facilitate rapid oxidation of bound Cu(i) to Cu(ii) (S. K. Singh, et al., J. Biol. Chem., 2011, 43, 37849-37857). The activities of variants featuring mutations at sites Cu5 (D360M, M355LD..