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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
 
 
 
 

The effects of the site-directed removal of N-glycosylation sites from beta-1,4-N-acetylgalactosaminyltransferase on its function.

The amino acid sequence deduced from the cloned human cDNA of beta-1,4-N-acetylgalactosaminyltransferase ( GalNAc-T; EC 2.4.1.92) gene predicted three potential sites for N-linked glycosylation. Although many glycosyltransferases isolated contain from 2 to 6 N-glycosylation sites, their significance has not been adequately demonstrated. To clarify the roles of N-glycosylation in GalNAc-T function, we generated a series of mutant cDNAs, in which some or all of the glycosylation recognition sites were eliminated by polymerase chain reaction (PCR)-mediated site-directed mutagenesis. Using transcription/translation in vitro, we confirmed that all potential N-glycosylation sites could be used. Although cell lines transfected with mutant cDNAs showed equivalent levels of GalNAc beta 1-->4(NeuAc alpha 2-->3)Gal beta 1-->4Glc-Cer (GM2) to that of the wild-type, the extracts from mutant cDNA transfectants demonstrated lower enzyme activity than in the wild-type. The decrease in enzyme activity was more evident as the number of deglycosylated sites increased, with about 90% decrease in a totally deglycosylated mutant. The enzyme kinetics analysis revealed no significant change of Km among wild-type and mutant cDNA products. The intracellular localization of GalNAc-T expressed in transfectants with wild-type or mutant cDNAs also showed a similar perinuclear pattern (Golgi pattern). These results suggest that N-linked carbohydrates on GalNAc-T are required for regulating the stability of the enzyme structure.[1]

References

  1. The effects of the site-directed removal of N-glycosylation sites from beta-1,4-N-acetylgalactosaminyltransferase on its function. Haraguchi, M., Yamashiro, S., Furukawa, K., Takamiya, K., Shiku, H., Furukawa, K. Biochem. J. (1995) [Pubmed]
 
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