NANS is a 359 amino acid protein that contains one AFP（antifreeze proteins)-like domain and functions in the biosynthesis of sialic acids. The ubiquitously expressed NANS enzymatically catalyzes the H2O-dependent formation of N-acetylneuraminic acid（Neu5Ac) and 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid（KDN)， both of which are sialic acids. NANS uses N-acetylmannosamine 6-phosphate as a substrate for Neu5Ac synthesis and mannose 6-phosphate as a substrate for KDN synthesis.
