Figure 17-36. Addition and initial processing of N-linked oligosaccharides in the rough ER of vertebrate cells.

Figure 17-36Addition and initial processing of N-linked oligosaccharides in the rough ER of vertebrate cells

The Glc3Man9(GlcNAc)2 precursor is transferred from the dolichol carrier to a susceptible asparagine residue on a nascent protein as soon as the asparagine crosses to the luminal side of the ER (step 1). In three separate reactions, first one glucose residue (step 2), then two glucose residues (step 3), and finally one mannose residue 4 are removed. Re-addition of one glucose residue (step 3a) is part of the ER quality-control process (see text). Following these reactions, the newly made protein is transported in a vesicle to the Golgi for further processing of the oligosaccharide (see Figure 17-38). [See R. Kornfeld and S. Kornfeld, 1985, Annu. Rev. Biochem. 45:631, and M. Sousa and A. J. Parodi, 1995, EMBO J. 14:4196.]

From: Section 17.7, Protein Glycosylation in the ER and Golgi Complex

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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