N-Acetylneuraminic acid (Neu5Ac or NANA) is the predominant sialic acid found in mammalian cells. This negatively charged residue is found in complex glycans on mucins and glycoproteins found at the cell membrane. Neu5Ac residues are also found in glycolipids, such as gangliosides, a crucial component of neuronal membranes found in the brain. Along with involvement in preventing infections (mucus associated with mucous membranes— mouth, nose, GI, respiratory tract), Neu5Ac acts as a receptor for influenza viruses, allowing attachment to mucous cells via hemagglutinin (an early step in acquiring influenzavirus infection).