In its thiocarboxylated form (CysO-COSH), is the sulfur donor in the CysM-dependent cysteine biosynthetic pathway. May be of particular importance for cysteine biosynthesis in the persistent phase of M.tuberculosis. Amino-acid biosynthesis; L-cysteine biosynthesis. Up-regulated under oxidative stress conditions. Thiocarboxylated by MoeZ. A covalent CysO-cysteine adduct is formed by the action of CysM. The structure of the adduct seems to be first a S-(glycyl)-cysteinate which leads to a N-(glycyl)-cysteinate after a S->N acyl shift. Native form. Thiocarboxylated form. CysO-cysteine adduct. Belongs to the sulfur carrier protein CysO family.