Abstract
Sucrase-isomaltase (SI) is a major microvillar glycoprotein of the small intestine. It is synthesized as a single polypeptide chain, which is extracellularly cleaved by pancreatic secretions to its two enzymatically active subunits sucrase (S) and isomaltase (I). We have Investigated the biosynthesis and maturation of this complex with particular emphasis on the glycosylation events. Enzymic and chemical deglycosylations of SI with endo-β-N-acetylglucosaminidase F (endo F) and trifluoromethanesulfonic acid (TFMS) as well as probing for the binding capacity of SI to Helix pomatia lectin demonstrated that pro-SI, I and S are N- and O-glycosylated. Furthermore, the results were indicative of a post-translational O-glycosylation of pro-SIh, since (i) the earliest detectable precursor form, pro-SIh, did not bind to H. pomatia lectin and (ii) its deglycosylation products with both endo-β-N-acetylglucosaminidase H (endo H) and TFMS were identical. Both the S and I subunits contain eight N-linked glycan units, at least one of which is of the high mannose type and found on S. Finally, S, but not I, was shown to display at least four populations varying in their content of O-linked glycans. The heterogeneous O-glycosylation pattern of S could be correlated with the distal position of this subunit (and its O-glycosylation sites) within the pro-SI molecule thus affecting the extent of O-linked oligosaccharide processing and their subsequent presentation on the mature molecule.
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Naim, H., Sterchi, E. & Lentze, M. 47 N- and O-GLYCOSYLATION OF HUMAN INTESTINAL SUCRASE-ISOMALTASE: DIFFERENTIAL O-GLYCOSYLATION OF THE SUCRASE SUBUNIT CORRELATES WITH ITS POSITION WITH IN THE ENZYME COMPLEX. Pediatr Res 24, 413 (1988). https://doi.org/10.1203/00006450-198809000-00070
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DOI: https://doi.org/10.1203/00006450-198809000-00070