Binding site for chitin oligosaccharides in the soybean plasma membrane

Affinity cross-linking of the plasma membrane fraction to an I-125-labeled chitin oligosaccharide led to the identification and characterization of an 85-kD, chitin binding protein in plasma membrane-enriched fractions from b oth suspension-cultured soybean cells and root tissue, inhibition analysis indicated a binding preference for larger (i.e. degrees of polymerization = 8) N-acetylated chitin molecules with a 50% inhibition of initial activity value of approximately 50 nM. N-Acetyl-glucosamine and chitobiose showed n o inhibitory effects at concentrations as high as 250 muM. it is noteworthy that the major lipo-chitin oligosaccharide Nod signal produced by Bradyrhi zobium japonicum was also shown to be a competitive inhibitor of ligand bin ding. However, the binding site appeared to recognize the chitin portion of the Nod signal, and it is unlikely that this binding activity, represents a specific Nod signal receptor. Chitooligosaccharide specificity for induct ion of medium alkalinization and the generation of reactive oxygen in suspe nsion-cultured cells paralleled the binding activity. Taken together, the p resence of the chitin binding protein in the plasma membrane fraction and t he specificity and induction of a biological response upon ligand binding s uggest a role for the protein as an initial response mechanism for chitin p erception in soybean (Glycine max).