Inhibition of the adenylylation of liver plasma membrane- bound proteins by plant and mammalian lectins

Journal/Book: Biol. Chem. Hoppe- Seyler 374 (2), 133-141. 1993;

Abstract: Liver plasma membrane contains four major (130-kDa, 120-kDa, 110-kDa and100-kDa) sialic acid-containing glycopolypeptides that are able toundergo adenylylation, as well as phosphorylation (San Jose et al.(1990) J. Biol. Chem. 265; 20653-20661). To gain insight into theregulation of these processes, lectins are employed to probe the extentof influence of their interaction with membrane fractions for thesereactions. We demonstrate that the beta-galactoside-specific lectinsfrom bovine heart and mistletoe at low concentrations inhibit theadenylylation of this set of plasma membrane glycopolypeptides. Theextent of phosphorylation of these polypeptides is also reduced althoughto a lesser degree. Concanavalin A, too, inhibits the adenylylation ofthe plasma membrane glycopolypeptides, although higher concentrations ofthis lectin were required, whereas wheat germ lectin has only a verysmall inhibitory effect. The adenylylable polypeptides were isolated byconcanavalin A-agarose chromatography upon elution with mannose. Inagreement with this result, control experiments with a panel ofneoglycoproteins indicate that mannose residues appear to be requiredfor the concanavalin A-induced inhibition of the adenylylation.Neoglycoproteins containing mannose 6-phosphate, lactose, fucose, orsialic acid instead of mannose lack the ability to protect theadenylylation from the inhibitory action of concanavalin A. In contrast,none of the above-mentioned neoglycoproteins, nor asialofetuin, norgalactose-containing saccharides protect the adenylylation against theinhibitory effect of both the mistletoe and bovine heart lectins,emphasizing the importance of either high affinity carbohydrate ligandsin the overall process, or other ligand sites for the lectins besidecarbohydrates to affect the regulation of the adenylylation system.Author.

Keyword(s): ALPHA-FETOPROTEINS/ME (metabolism)

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