Abstract
Three cysteine desulfurases-IscS, CsdA, and SufS-of Escherichia coli can transfer sulfur from L-cysteine to the C-terminal carboxylate of the smaller subunit of molybdopterin synthase to yield a thiocarboxylate group in a defined in vitro system for the generation of the dithiolene group of molybdopterin from precursor Z, which is an oxygen-sensitive tetrahydropyranopterin and the immediate precursor of molybdopterin in molybdenum cofactor biosynthesis. In this study, we report that an iscS-deletion strain of E. coli accumulates compound Z, a direct oxidation product of precursor Z, to the same extent as a ΔmoaD strain. In contrast, analysis of the content of compound Z in ΔsufS and ΔcsdA strains revealed no such accumulation. These findings suggest that IscS is the primary sulfur-donating enzyme for the generation of the thiocarboxylate of molybdopterin synthase in molybdopterin biosynthesis.
