Maturational changes in terminal glycosylation of small intestinal microvillar proteins in the rat

Abstract

Studies were performed to identify rat intestinal microvillar proteins which undergo changes in terminal glycosylation during postnatal development. Pulse-labeling with [ 3H]fucose or N-[ 3H] acetylgalactosamine showed significantly higher incorporation into purified microvillar membranes of weanling than suckling rats. In contrast, the incorporation of [ 3H]sialic acid after pulse-labeling with N-[ 3H] acetylmanosamine was higher in suckling rats. SDS-polyacrylamide gel electrophoresis revealed these developmental differences in radioactive sugar incorporation to involve mainly proteins above M r 90000. 125I-labeled peanut lectin autoradiography revealed an M r > 330000 binding protein in suckling rats. Neuraminidase treatment of the membranes revealed the presence of sialyl-substituted sites in this protein in suckling, weaning and weanling animals, but the unmasking of sites decreased with advancing maturation. 125I-labeled Ulex europeus I autoradiography showed marked increases in binding of this lectin to M r 66000, 92000, 130000, 150000 and > 333000 proteins from weaning to weanling periods. Similar age-related increases in soybean lectin binding to M r 130000–150000, and > 330000 proteins were demonstrated by affinity chromatography. The M r values of the major lectin-binding proteins were close to those reported for several hydrolases (trehalase, alkaline phosphatase, sucrase-isomaltase and glucoamylase). Comparison of the Coomassie blue-stained electrophoretograms from each age-group against the corresponding autoradiograms of lection-binding proteins led us to conclude that, while the content of these proteins in the membrane achieve their mature levels at or before weaning, their terminal glycosylation (desialylation, fucosylation, N-acetylgalactosamination) is not fully established until later development.