Sulfur incorporation into the molybdenum cofactor (Moco) in the Gram-negative bacterium Escherichia coli involves six enzymes. The initial reaction includes the cysteine desulfurase IscS, the sulfurtransferase TusA, and the rhodanese domaincontaining protein YnjE. The Gram-positive bacterium Bacillus subtilis contains no direct homologs for IscS, but rather four distinct cysteine desulfurases (YrvO, NifS, NifZ, SufS) and YrkF, a two-domain rhodanese protein with an N-terminal domain similar to TusA. Bioinformatic analysis was used to identify potential enzymes involved in the B. subtilis Moco thiolation pathway and in vitro reactions demonstrated that YrkF can accept sulfur from and enhance the activity of YrvO.
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