Escherichia coli MoeA and MogA -: Function in metal incorporation step of molybdenum cofactor biosynthesis

Escherichia coli MoeA and MogA are required for molybdenum cofactor biosynthesis and are believed to function in the addition of molybdenum to the dithiolene of molybdopterin to form molybdenum cofactor. Here we show that moeA(-) and mogA(-) cells are able to synthesize molybdopterin, but both are deficient in molybdenum incorporation and, as a consequence, are deficient in the formation of molybdopterin-guanine dinucleotide. Human sulfite oxidase expressed in E. coli moeA(-) could be activated in vitro in the presence of MoeA and low concentrations of molybdate. Sulfite oxidase purified from the moeA(-) lysate was also activated, although to a lesser extent than observed in the presence of lysate. MogA was incapable of activating sulfite oxidase expressed in E. coli mogA(-). These results demonstrate that molybdenum insertion into molybdopterin is required for molybdopterin-guanine dinucleotide formation, and that MoeA facilitates molybdenum incorporation at low levels of molybdate, but MogA has an alternative function, possibly as a carrier for molybdopterin during molybdenum incorporation.