The Role of System-Specific Molecular Chaperones in the Maturation of Molybdoenzymes in Bacteria

Figure 6

Model for the role of XdhC in the assembly of R. capsulatus XDH. The assembly of R. capsulatus XDH involves the synthesis of the XdhA and XdhB subunits, the dimerization of both subunits, the insertion of FeSI, FeSII, and FAD into the XdhA subunit, dimerization of two (αβ) dimers via the XdhB subunit to form the Moco-free apo-XDH, and finally, insertion of sulfurated Moco into XdhC. Mo-MPT is produced by molybdenum insertion into MPT catalyzed by MogA and MoeA and can further be converted to bis-MGD by the MobA protein. It is suggested that MoeA/MogA/MobA and XdhC form a complex in the cell. XdhC binds Mo-MPT, and the equatorial Mo=S is inserted into Moco before its incorporation into XDH by the sulfurtransferase function of the NifS4 protein. XdhC protects Moco from oxidation and interacts with XDH for Moco insertion.