Rhesus monkey gastric mucins: oligomeric structure, glycoforms and Helicobacter pylori binding

Abstract

Mucins isolated from the stomach of Rhesus monkey are oligomeric glycoproteins with a similar mass, density, glycoform profile and tissue localization as human MUC5AC and MUC6. Antibodies raised against the human mucins recognize those from monkey, which thus appear to be orthologous to those from human beings. Rhesus monkey muc5ac and muc6 are produced by the gastric-surface epithelium and glands respectively, and occur as three distinct glycoforms. The mucins are substituted with the histo blood-group antigens B, Le^a (Lewis a), Le^b, Le^x, Le^y, H-type-2, the Tn-antigen, the T-antigen, the sialyl-Le^x and sialyl-Le^a structures, and the expression of these determinants varies between individuals. At neutral pH, Helicobacter pylori strains expressing BabA (blood-group antigen-binding adhesin) bind Rhesus monkey gastric mucins via the Le^b or H-type-1 structures, apparently on muc5ac, as well as on a smaller putative mucin, and binding is inhibited by Le^b or H-type-1 conjugates. A SabA (sialic acid-binding adhesin)-positive H. pylori mutant binds to sialyl-Le^x-positive mucins to a smaller extent compared with the BabA-positive strains. At acidic pH, the microbe binds to mucins substituted by sialylated structures such as sialyl-Le^x and sialylated type-2 core, and this binding is inhibited by DNA and dextran sulphate. Thus mucin–H. pylori binding occurs via at least three different mechanisms: (1) BabA-dependent binding to Le^b and related structures, (2) SabA-dependent binding to sialyl-Le^x and (3) binding through a charge-mediated mechanism to sialylated structures at low pH values.