The Biosynthesis of the Molybdenum Cofactor in Escherichia coli and Its Connection to FeS Cluster Assembly and the Thiolation of tRNA

Figure 1

The different structures of Moco in E. coli. The basic form of Moco is a 5,6,7,8-tetrahydropyranopterin with a unique dithiolene group coordinating the molybdenum atom, named Mo-MPT. Mo-MPT (shown in the tri-oxo structure [25]) can be further modified and in E. coli three different molybdenum-containing enzyme families exist classified according to their coordination at the molybdenum atom: the xanthine oxidase, sulfite oxidase, and DMSO reductase families. In E. coli, the xanthine oxidase family contains the sulfurated MCD cofactor. The sulfite oxidase family is characterized by a di-oxo Moco with an additional protein ligand, which usually is a cysteine. The DMSO reductase family contains two MGDs ligated to one molybdenum atom with additional ligands being an O/S and a sixth ligand X, which can be a serine, a cysteine, a selenocysteine, an aspartate or a hydroxide, and/or water molecule. The characterized molybdoenzymes in E. coli are shown in blue for each family.