<b>Plant chitinase/lysozyme isoforms show distinct substrate specificity and cleavage site preference towards lipochitooligosaccharide Nod signals</b>

Abstract

Summary The ability of 16 chitinases from seven different plant species to hydrolyze a collection of several structurally related lipochitooligosaccharides (LCOs) of Rhizobium was analyzed. It was found that the enzymes differed to a large extent in their activity on different LCOs. Differences were attributed to (i) the relative activity on different LCOs as substrate (e.g. sulfated versus non‐sulfated LCOs); (ii) the relative cleavage site preference on a given LCO molecule (hydrolysis of either the second, third or fourth glycosidic bond from the non‐reducing end of the molecule); and (iii) the stereochemistry of the reaction (retention or inversion of the anomeric configuration). A graphic representation of the different substrate specificities resulted in a ‘fingerprint’ that is characteristic for a given enzyme or a family of related enzymes. By comparing the LCO‐fingerprint of unknown enzymes with those obtained for already characterized proteins, it is possible to identify new glycosyl hydrolases. The high diversity of substrate specificity found among plant chitinases may reflect variations in the natural substrates of the enzymes, such as substitutions on the chitin moiety of fungal cell walls or, in plants, the presence of putative endogenous substrates related to LCOs.