Sialic Acid Synthase (NANS) is an enzyme that contains one AFP-like domain. NANS is ubiquitous and plays a role in the biosynthetic pathways of sialic acids. NANS produces N-acetylneuraminic acid (Neu5Ac) and 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN). It also can use N-acetylmannosamine 6-phosphate and mannose 6-phosphate as substrates to generate phosphorylated forms of Neu5Ac and KDN, respectively.