Catalyzes the removal of elemental sulfur from cysteine to produce alanine (Probable). Binds 1 2Fe-2S cluster per subunit in a crystal formed under reducing conditions; this subunit provides 1 ligand while IscU provides the other 3 ligands. It is likely that Fe-S cluster coordination is flexible as the role of this complex is to build and then hand off Fe-S clusters. [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Cofactor affinity is increased in an IscS-IscU complex. Cofactor biosynthesis; iron-sulfur cluster biosynthesis. Forms a heterotetramer with IscU, interacts with other sulfur acceptors. In Archaea the pyridoxal phosphate cofactor is not covalently bound to Lys but ligated by other amino acids. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. NifS/IscS subfamily.