Alteration of oligosaccharide biosynthesis by genetic manipulation of glycosyltransferases.
The alteration of oligosaccharide structures through genetic manipulation of glycosyltransferase activities is now a reality. It is apparent that this technique has greater consequences on oligosaccharide structure when an exogenous enzyme is introduced into cells, and in particular when this enzyme is responsible for a terminal glycosylation step. By contrast, only one study has examined the effects of overexpressing an endogenous glycosyltransferase, in which there was no detectable effect on glycosylation. However, there are still other key regulatory biosynthetic enzymes, such as GlcNAc transferase V and beta 1,3 GlcNAc transferase, whose overexpression may alter glycosylation. Both of these enzymes are required for the biosynthesis of polylactosaminoglycans (polymers of N-acetyllactosamine disaccharides), and their elevation in tumor cells correlates with increased expression of polylactosaminoglycans. Recently, the gene encoding GlcNAc transferase V has been isolated, but its transfection into cells and characterization of the resulting oligosaccharides awaits further study. Alternate strategies for modifying oligosaccharide structures could involve the introduction of more than one glycosyltransferase into cells to ensure the availability of biosynthetic intermediates. Alternatively, the disruption of specific glycosyltransferase genes by homologous recombination could be used to eliminate competing glycosyltransferases that act on a common substrate. Although oligosaccharide biosynthesis is directly dependent upon the presence or absence of specific glycosyltransferases, other factors also contribute to glycosylation. For example, the transport rate of a glycoprotein through the endoplasmic reticulum and Golgi complex, the levels of processing glycosidases, the availability of substrates, the host cell, and ultimately, the peptide backbone of the particular glycoprotein of interest are important contributors to the final outcome of oligosaccharide structure. Despite these complications, further study into the manipulation of glycosyltransferase genes may ultimately allow the controlled and predictable biosynthesis of glycoprotein sugar chains.
Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030.
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Youakim
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Shur
D000818:Animals; D016466:CHO Cells; D002240:Carbohydrate Sequence; D002478:Cells, Cultured; D006224:Cricetinae; D018076:DNA, Complementary / Q000235:genetics; D006031:Glycosylation; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism; D009844:Oligosaccharides / Q000096:biosynthesis*; D015202:Protein Engineering; D011993:Recombinant Fusion Proteins / Q000378:metabolism*
D018076:DNA, Complementary; D009844:Oligosaccharides; D011993:Recombinant Fusion Proteins; D016695:Glycosyltransferases; D017351:N-Acetylglucosaminyltransferases; C063057:UDP-N-acetylglucosamine-peptide beta-N-acetylglucosaminyltransferase