Structure of the flavocytochrome c c sulfide dehydrogenase associated with the copper‐binding protein CopC from the haloalkaliphilic sulfur‐oxidizing bacterium Thioalkalivibrio paradoxus Thioalkalivibrio paradoxus ARh 1

摘要

Flavocytochrome c sulfide dehydrogenase from Thioalkalivibrio paradoxus ( Tp FCC) is a heterodimeric protein consisting of flavin‐ and monohaem c ‐binding subunits. Tp FCC was co‐purified and co‐crystallized with the dimeric copper‐binding protein Tp CopC. The structure of the Tp FCC–( Tp CopC) 2 complex was determined by X‐ray diffraction at 2.6?? resolution. The flavin‐binding subunit of Tp FCC is structurally similar to those determined previously, and the structure of the haem‐binding subunit is similar to that of the N‐terminal domain of dihaem FCCs. According to classification based on amino‐acid sequence, Tp CopC belongs to a high‐affinity CopC subfamily characterized by the presence of a conserved His1‐Xxx‐His3 motif at the N‐terminus. Apparently, a unique α‐helix which is present in each monomer of Tp CopC at the interface with Tp FCC plays a key role in complex formation. The structure of the copper‐binding site in Tp CopC is similar to those in other known CopC structures. His3 is not involved in binding to the copper ion and is 6–7?? away from this ion. Therefore, the His1‐Xxx‐His3 motif cannot be considered to be a key factor in the high affinity of CopC for copper(II) ions. It is suggested that the Tp FCC–( Tp CopC) 2 heterotetramer may be a component of a large periplasmic complex that is responsible for thiocyanate metabolism.