Investigation of gliadin binding to different selected proteins using a biotin-streptavidin system (1)
Binding of gliadins to constituents of the coeliac patients’ mucosa may represent one of the decisive steps in the pathogenesis of the disease and has already been investigated repeatedly. An unspecific binding, in terms of other peptides showing a similar behaviour.
From the 19 proteins investigated four bound strongly (ODmax > 1.2; casein, mucin fibronectin, fibrinogen), eight were found to bind with medium strength (ODmax > 0.5; fetuin, myoglobin, cytochrome C, ovalbumin, human gamma-globulin, Ulex europaeus agglutinin, goat immunoglobulins, human apoproteins), and seven bound weakly (ODmax<0.5; concanavalin A, bovine serum albumin, soybean lectin, ferritin, phytohaemagglutinin, invertase, peroxidase) to gliadin.
Proteins bound to gliadin could also be shown to associate with different gliadin subfractions. Binding was demonstrable, too, after gliadin had been partially hydrolysed using different proteases, with the exception of PT-gliadin and of fraction 9, which no longer associated with ovalbumin.
Only binding of casein was inhibited by sialic acid and only that of mucin by N-acetylglucosamine.
The binding of all but one of 11 test proteins to gliadin was inhibited strongly by ethylene glycol and dioxane, and in the case of goat immunoglobulin and human gamma-globulins the inhibition exerted by dioxane was nearly complete. Tween 20 and Triton X-100 were strongly effective in inhibiting the association with gliadin of eight out of nine or ten proteins.
Carbohydrates seem to be without a general role for binding because:
1. There are ligands known to be glycoproteins in the group of binding (fetuin, mucin, casein, ovalbumin, fibrinogen, and immunoglobulins) as well as in the group of non-binding proteins (peroxidase and invertase).
2. Different lectins do not bind.
3. There is no consistent effect of at least one of the investigated sugars on binding of four different glycoproteins to gliadin.