A diverse range of bacterial and eukaryotic chitinases hydrolyze the LacNAc (Gal{beta}1-4GlcNAc) and LacdiNAc (GalNAc{beta}1-4GlcNAc) motifs found on vertebrate and insect cells [Enzymology]

January 5th, 2015 by Frederiksen, R. F., Yoshimura, Y., Storgaard, B. G., Paspaliari, D. K., Petersen, B. O., Chen, K., Larsen, T., Duus, J. O., Ingmer, H., Bovin, N. V., Westerlind, U., Blixt, O., Palcic, M. M., Leisner, J. J.

There is emerging evidence that chitinases have additional functions beyond degrading environmental chitin, such as involvement in innate and acquired immune responses, tissue remodeling, fibrosis and serving as virulence factors of bacterial pathogens. We have recently shown that both the human chitotriosidase and a chitinase from Salmonella enterica serovar Typhimurium hydrolyze LacNAc from Galβ1-4GlcNAcβ-tetramethylrhodamine (LacNAc-TMR1), a fluorescently labelled model substrate for glycans found in mammals. In this study, we have examined the binding affinities of the Salmonella chitinase by carbohydrate microarray screening and found that it binds to a range of compounds, including five that contain LacNAc structures. We have further examined the hydrolytic specificity of this enzyme and chitinases from Sodalis glossinidius and Polysphondylium pallidum, which are phylogenetically related to the Salmonella chitinase, as well as unrelated chitinases from Listeria monocytogenes using the fluorescently labelled substrate analogs LacdiNAc-TMR (GalNAcβ1-4GlcNAcβ-TMR), LacNAc-TMR and LacNAcβ1-6LacNAcβ-TMR. We found that all chitinases examined hydrolyzed LacdiNAc from the TMR aglycone to various degrees, while they were less active towards LacNAc-TMR conjugates. LacdiNAc is found in the mammalian glycome and is a common motif in invertebrate glycans. This substrate specificity was evident for chitinases of different phylogenetic origins. Three of the chitinases also hydrolyzed the β1-6 bond in LacNAcβ1-6LacNAcβ-TMR, an activity that is of potential importance in relation to mammalian glycans. The enzymatic affinities for these mammalian-like structures suggest additional functional roles of chitinases beyond chitin hydrolysis.
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