Developmental profile of neural cell adhesion molecule glycoforms with a varying degree of polymerization of polysialic acid chains

More precise information on the degree of polymerization (DP) of polysialie acid (polySia) chains expressed on neural cell adhesion molecule (NCAM) and its developmental stage-dependent variation are considered important in understanding the mechanism of regulated polysialylation and fine-tuning of NCAM-mediated cell adhesion by polySia. In this paper, first we performed a kinetic study of acid-catalyzed hydrolysis of polySia and report our findings that (a) in (--> 8Neu5Ac alpha2 -->)(n)--> 8Neu5Ac alpha2 --> 3Gal beta1 -->R, the proximal Neu5Ac residue alpha2 -->3 linked to Gal is cleaved about 2.5-4 times faster than the alpha2 -->8 linkages and (b) in contrary to general belief that alpha2 -->8 linkages in polySia are extremely labile, the kinetic consideration showed that they are not so unstable, and every ketosidic bond is hydrolyzed at the same rate. These findings are the basis of our strategy for DP analysis of polySia on NCAM. Second, using the recently developed method that provides base-line resolution of oligo/polySia from DP 2 to > 80 with detection thresholds of 1.4 fmol per resolved peak, we have determined the DP of polySia chains expressed in embryonic chicken brains at different developmental stages. Our results support the presence of numerous NCAM glycoforms differing in DPs of oligo/polySia chains and a delicate change in their distribution during development.