Multiple roles of TorD-like chaperones in the biogenesis of molybdoenzymes

Biogenesis of prokaryote molybdoenzymes is a complex process leading to the insertion of the molybdenum cofactor in the cytoplasm into a folded apoenzyme before transport through the cell membrane. Usually, specific chaperones belonging to the TorD family are required for the maturation of the molybdoenzymes of the dimethyl sulfoxide reductase family. These chaperones play a crucial role during the biogenesis and the incorporation of the molybdenum cofactor by interacting with the core of the apoprotein. Moreover, they are also involved in the protection of the apoproteins by binding to their N-terminal extremity in an early stage of synthesis. Finally, the TorD-like proteins may possess a proofreading activity and they could target their partners to the twin arginine translocation machinery system for cross-membrane transport of prefolded proteins. The roles of these chaperones during the different steps of molybdoenzyme biogenesis are described.