What is "polysialic acid"

n. (context biochemistry English) A polymeric form of sialic acid that is involved in cell adhesion

Polysialic acid is an unusual posttranslational modification that occurs on neural cell adhesion molecules (NCAM). Polysialic acid is considerably anionic. This strong negative charge gives this modification the ability to change the protein's surface charge and binding ability. In the synapse, polysialation of NCAM prevents its ability to bind to NCAM's on the adjacent membrane.