Serine-glycine hydroxymethyltransferase (SHMT). This family belongs to pyridoxal phosphate (PLP)-dependent aspartate aminotransferase superfamily (fold I). SHMT carries out interconversion of serine and glycine; it catalyzes the transfer of hydroxymethyl group of N5, N10-methylene tetrahydrofolate to glycine resulting in the formation of serine and tetrahydrofolate. Both eukaryotic and prokaryotic SHMT enzymes form tight obligate homodimers; the mammalian enzyme forms a homotetramer comprising four pyridoxal phosphate-bound active sites.