POLY-N-ACETYLLACTOSAMINE-SPECIFIC TOMATO LECTIN INTERACTS WITH GASTRIC PARIETAL-CELLS - IDENTIFICATION OF A TOMATO-LECTIN BINDING 60-90X103MR MEMBRANE GLYCOPROTEIN OF TUBULOVESICLES

  • 1 April 1990
    • journal article
    • research article
    • Vol. 95, 563-+
Abstract
The cytoplasmic tubulovesicular and canalicula membranes of gastric parietal cells are intimately involved in hydrochloric acid secretion. To characterize the glycoproteins of these membranes, we examined a panel of lectins for reactivity with parietal cells in paraffin sections of rat, dog and pig stomach. The poly-N-acetyllactosamine-specific lectin from Lycopersicon esculentum (tomato) and from Solanum tuberosum (potato), and the galactose-specific lectin Ricinus communis agglutinin (RCA120), showed strong cytoplasmic binding of parietal cells of all three species, with a pattern indicative of an intracellular membrane network. Binding to parietal cells was confirmed by double-labelling studies with parietal cell auto-antibodies from patients with autoimmune gastritis. Mucous cells and mucin also bound these lectins strongly. Other gastric cell types did not stain with either tomato or potato lectin, but stained weakly with RCA120. Electron-microscopic examination of lectin binding sites using biotinylated tomato lectin or RCA120 and streptavidin-gold, revealed specific binding to the luminal face of parietal cell tubulovesicular and canalicular membranes as well as the contents of mucous cell secretory granules. Tomato lectin and RCA120 reacted by lectin blotting with a major species of apparent molecular weight 60-90 .times. 103 Mr from rat, dog and pig gastric membranes. A tubulovesicular membrane fraction, enriched 10-fold for K+-dependent phosphatase activity, was also enriched three-fold for tomato lectin binding as assessed by a solid-phase lectin assay. The 60-90K (K = 103 Mr) component, in 125I-labelled detergent extracts of dog tubulovesicular membranes, bound to an affinity support of tomato lectin-Sepharose and was specifically eluted with N,N'',N''-triacetylchitotriose. Digestion with N-glycanase collapsed the 60-90K component into a sharp 35K band. We conclude that: (1) a 60-90K membrane glycoprotein localized on the luminal face of tubulovesicles and canaliculi of parietal cells interacts strongly with tomato lectin and RCA120; and (2) the glycoprotein is composed of a 35K core protein glycosylated with N-glycans probably containing poly-N-acetyllactosamine sequences with terminal galactosyl residues. The properties of this 60-90K glycoprotein are identical to a major parietal cell autoantigen recognized by sera of patients with autoimmune gastritis. As this molecule represents the only component other than the 95K catalytic subunit of the H+/K+-ATPase, which has been specifically identified with parietal cell tubulovesicles, and as it has a similar sized protein core to that of the .beta. subunit of the Na+/K+-ATPase, we propose that it is the .beta. subunit of the proton pump.

This publication has 22 references indexed in Scilit: