Sialic acid synthetase (N-acetylneuraminate synthase or N-acetylneuraminate-9-phosphate synthase) catalyzes the condensation of phosphoenolpyruvate with N-acetylmannosamine (ManNAc, in bacteria) or N-acetylmannosamine-6-phosphate (ManNAc-6P, in mammals), to yield N-acetylneuramic acid (NeuNAc) or N-acetylneuramic acid-9-phosphate (NeuNAc-9P), respectively. The N-terminal NeuB domain, a TIM-barrel-like structure, contains the catalytic site, the function of the SAF domain is not as clear. It may participate in domain-swapped dimerization and play a role in binding the substrate, in either domain-swapped dimers or by directly interacting with the N-terminal domain. Also included in the family are PEP-sugar pyruvyltransferases known as spore coat polysaccharide biosynthesis proteins (SpsE).
Jiyao W et al.(2023). "The conserved domain database in 2023.",