Abstract
Cysteine has been shown to be the source of sulfur for the biosyntheses of a variety of cofactors including biotin, lipoic acid, molybdopterin, and thiamine, as well as Fe-S clusters in proteins and thionucleosides in tRNA. Although the source has been identified, the biochemical steps for sulfur incorporation into these molecules are poorly understood. However, recent studies have provided evidence that a pyridoxal 5^1-phosphate-dependent cysteine desulfurase is involved in the initial stages of sulfur trafficking within cells. Cysteine desulfurase is a homodimeric enzyme which catalyzes the conversion of L-cysteine to L-alanine and sulfane sulfur via the formation of a protein-bound cysteine persulfide intermediate on a conserved cysteine residue. The persulfide intermediate donates sulfur to Fe-S clusters, thiamine, and thionucleosides in tRNA. The enzyme is also proposed to be involved in cellular iron homeostasis and in the biosynthesis of selenoproteins. This paper describes recent developments in the study of cysteine desulfurases.
