Phosphoserine aminotransferases is a pyridoxal phosphate dependent enzyme converting O-phospho-L-serine and oxoglutarate to 3-phosphonooxypyruvate and L-glutamate in the major phosphorylated serine biosynthesis pathway. The enzyme is part of the aminotransferase class-V family. The protein structure is a dimer with each subunit consisting of a small and a large domains. The large domain spans residues of 64 – 262 with seven-stranded beta-sheets and four alpha-helices all in one side contacting the same region of the other subunit. The rest of the monomer forms the small domain and between the two domains in a relatively wide open surface, a pyridoxal phosphate binds to a largely positively charged shallow patch.