Structure and analysis of a virulent chitinase from Listeria monocytogenes.

Listeria monocytogenes is the causative agent of Listeriosis, a serious foodborne illness that primarily affects pregnant women, new-borns, the elderly, and immunocompromised individuals. L. monocytogenes secretes proteins that bind and degrade chitin, a linear polysaccharide formed of β1,4-linked N-acetylglucosamine residues, and although humans do not produce chitin, these enzymes act as virulence factors that promote bacterial growth during host infection. The chitinase ChiA is a major contributor to virulence, and it can modulate host immunity through downregulating the expression of host inducible nitric oxide synthase (iNOS), although this precise mechanism has yet to be determined. Here we present the X-ray crystal structure of L. monocytogenes ChiA at 1.95 Å resolution, complemented by solution small angle X-ray scattering analysis and molecular dynamics simulations. Our comparative analyses reveal structural conservation with homologous bacterial chitinases and highlight potential alternative ligand-binding sites beyond the canonical chitin-binding channel. Molecular dynamics simulations of an N-glycopeptide model demonstrate stable interactions between LmChiA and the mannose-rich N-glycan core near these putative sites. These findings suggest that LmChiA may interact with branched host glycans rather than exclusively processing chitin-derived substrates, and this provides a potential explanation for its role in modulating host immune responses.