Identification of the N-acetylneuraminyllactose-specific laminin-binding protein of Helicobacter pylori.

The interaction of the gastroduodenal pathogen Helicobacter pylori with the glycoprotein laminin was investigated. Binding of 125I-radiolabelled laminin in a liquid-phase assay by both hemagglutinating and poorly hemagglutinating strains was rapid, saturable, specific, partially reversible, of high affinity, and insensitive to pH. Inhibition of laminin binding by fetuin, but not asialofetuin, and reduced bacterial binding to periodate- or sialidase-treated laminin indicated that glycosylation, particularly sialylation, was important for laminin binding by H. pylori. Inhibition experiments with monosaccharides, disaccharides, and trisaccharides showed that the strains bound to a region spanning a trisaccharide. In particular, inhibition and displacement studies showed that binding to the trisaccharide N-acetylneuraminyl-alpha(2-3)-lactose [NeuAc(2-3)Lac] was preferential to that to the NeuAc(2-6)Lac isomer. Complete inhibition of laminin binding by both hemagglutinating and poorly hemagglutinating strains was achieved only when isolated lipopolysaccharide (LPS) was used as an inhibitor in combination with heat or protease treatment of H. pylori cells, thereby confirming the involvement of both LPS and a protein adhesin in laminin binding. Further inhibition experiments indicated that the protein receptor, rather than LPS, on H. pylori bound NeuAc(2-3)Lac. By using a Western blotting procedure, a 25-kDa outer membrane protein was identified as mediating laminin binding by both hemagglutinating and poorly hemagglutinating H. pylori strains. The specificity of binding was confirmed by complete inhibition of laminin binding by the 25-kDa protein with NeuAc(2-3)Lac. The data collectively suggest that a 25-kDa outer membrane protein acts in a lectin-like manner with LPS to mediate attachment of H. pylori to laminin.