MOCS2 is a heterotetrameric synthase composed of two small (MOCS2A) and two large (MOCS2B) subunits. The large and small subunits of molybdopterin synthase are both encoded from this gene by overlapping open reading frames. MOCS2 functions in the second step of the synthesis of molybdenum cofactor or molybdopterin (MPT). It catalyzes the formation of MPT from precursor Z by incorporating a dithiolene functional group.