ST6GalNAc-III is a relatively small sialyltransferase (305 amino acids in length) compared with other sialyltransferases characterized to date. Like other sialyltransferases, ST6GalNAc-III exhibits type II membrane protein topology and has characteristic motifs for sialyltransferases called sialylmotifs L, S, and VS. ST6GalNAc-III-VI are the members of one ST6GalNAc subfamily that can synthesize the ganglioside GDIα from GM1b (Sjoberg et al. 1996; Lee et al. 1999; Okajima et al. 1999, 2000; Ikehara et al. 1999). GD1α has been implicated as a molecular component of a variety of important biological processes. The overall amino acid sequence identity of mouse ST6GalNAc- III is 94.4% to rat ST6GalNAc-III, 43.0% to mouse ST6GalNAc-IV, 42.6% to mouse ST6GalNAc-V, and 41.4% to mouse ST6GalNAc-VI, but ST6GalNAc-III shows no significant similarity to other sialyltransferases except in sialylmotifs. This ST6GalNAc subfamily (ST6GalNAc-III-VI) has been suggested to have a different domain structure to other sialyltransferases (Lee et al. 1999; Okajima et al. 1999, 2000; Ikehara et al. 1999). ST6GalNAc-III, -V, and -VI prefer glycolipids to O-glycans as substrates, while ST6GalNAc-IV prefers O-glycans to glycolipids. Each gene has different tissue- specific expression patterns, suggesting that there may be several tissue-specific ST6GalNAc members capable of synthesizing GD1α.
KeywordsSialic Acid Competitive Polymerase Chain Reaction Embryonal Carcinoma Cell Line Mouse Embryonal Carcinoma Cell Ganglioside GD1a
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