Interactions with sulfur acceptors modulate the reactivity of cysteine desulfurases and define their physiological functions.

Sulfur-containing biomolecules such as [FeS] clusters, thiamin, biotin, molybdenum cofactor, and sulfur-containing tRNA nucleosides are essential for various biochemical reactions. The amino acid l-cysteine serves as the major sulfur source for the biosynthetic pathways of these sulfur-containing cofactors in prokaryotic and eukaryotic systems. The first reaction in the sulfur mobilization involves a class of pyridoxal-5'-phosphate (PLP) dependent enzymes catalyzing a Cys:sulfur acceptor sulfurtransferase reaction. The first half of the catalytic reaction involves a PLP-dependent CS bond cleavage, resulting in a persulfide enzyme intermediate. The second half of the reaction involves the subsequent transfer of the thiol group to a specific acceptor molecule, which is responsible for the physiological role of the enzyme. Structural and biochemical analysis of these Cys sulfurtransferase enzymes shows that specific protein-protein interactions with sulfur acceptors modulate their catalytic reactivity and restrict their biochemical functions.