Differential affinity of BsSCO for Cu(II) and Cu(I) suggests a redox role in copper transfer to the CuA center of cytochrome c oxidase

Abstract

SCO (synthesis of cytochrome c oxidase) proteins are involved in the assembly of the respiratory chain enzyme cytochrome c oxidase acting to assist in the assembly of the Cu(A) center contained within subunit II of the oxidase complex. The Cu(A) center receives electrons from the reductive substrate ferrocytochrome c, and passes them on to the cytochrome a center. Cytochrome a feeds electrons to the oxygen reaction site composed of cytochrome a(3) and Cu(B). Cu(A) consists of two copper ions positioned within bonding distance and ligated by two histidine side chains, one methionine, a backbone carbonyl and two bridging cysteine residues. The complex structure and redox capacity of Cu(A) present a potential assembly challenge. SCO proteins are members of the thioredoxin family which led to the early suggestion of a disulfide exchange function for SCO in Cu(A) assembly, whereas the copper binding capacity of the Bacillus subtilis version of SCO (i.e., BsSCO) suggests a direct role for SCO proteins in copper transfer. We have characterized redox and copper exchange properties of apo- and metalated-BsSCO. The release of copper (II) from its complex with BsSCO is best achieved by reducing it to Cu(I). We propose a mechanism involving both disulfide and copper exchange between BsSCO and the apo-Cu(A) site. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.

Thioredoxin‐like protein TlpA from Bradyrhizobium japonicum is a reductant for the copper metallochaperone ScoI

“…Finally, protein thiol:disulfide oxidoreductase activity has been demonstrated for Sco1‐like proteins from Rhodobacter sphaeroides and Pseudomonas putida [10,11]. One of the substrates was Cu 2+ , which became reduced to Cu + , an activity that had been reported also for the BsSco protein from Bacillus subtilis [12].…”

A Copper Relay System Involving Two Periplasmic Chaperones Drives cbb3-Type Cytochrome c Oxidase Biogenesis in Rhodobacter capsulatus

“…29,33 An exception is the Bacillus subtilis ScoI homologue, which seems to have approximately picomolar affinity for Cu(II), but only approximately micromolar affinity for Cu(I). 31,34 The basis of this difference is unclear, although the Gram-positive bacterium B. subtilis lacks a PccA homologue that could transfer Cu(I) to ScoI. Perhaps preferential binding of Cu(II) by B. subtilis ScoI in an oxidizing environment, such as the extracellular face of the membrane, might be beneficial in this case.…”

The Cu chaperone CopZ is required for Cu homeostasis in Rhodobacter capsulatus and influences cytochrome cbb3 oxidase assembly

“…The co‐expression of CopZ increased the activity of a heterologously expressed CotA laccase (Gunne et al , ), indicating a potential role of CopZ in Cu insertion into CotA. On the other hand, a deletion of copZ in B. subtilis did not influence aa 3 ‐type cytochrome oxidase ( aa 3 ‐Cox) activity (Radford et al , ), in agreement with the occurrence of dedicated Cu chaperones, like CtaG or Sco1, for aa 3 ‐Cox assembly (Bengtsson et al , ; Hill and Andrews, ). However, in Rhodobacter species, the cbb 3 ‐Cox and aa 3 ‐Cox assembly pathways do not engage identical Cu uptake and trafficking conduits (Khalfaoui‐Hassani et al , ; ).…”