Identification and characterization of endo- and exo-hydrolases cleaving the α- and β-D-arabinofuranosidic bonds of lipoarabinomannan and arabinogalactan of Mycobacteria

Abstract

Abstract Cell walls of pathogenic and acidophilic bacteria, such as Mycobacterium tuberculosis and Mycobacterium leprae, comprise lipoarabinomannan and arabinogalactan, which are composed of D-arabinose, the enantiomer of the typical l-arabinose found in plants. Their unusual glycan structures serve to immune-evasive of pathogenic mycobacteria. In this study, we identified four enzymes (two GHxxx endo-d-arabinanases, GH172 exo-α-D-arabinofuranosidase, and GH116 exo-β-D-arabinofuranosidase) from Microbacterium arabinogalactanolyticum that degrade the D-arabinan core structure of lipoarabinomannan and arabinogalactan. These enzymes completely degraded the complex glycans in a concerted manner. Furthermore, based on biochemical characterization using synthetic substrates and X-ray crystallography, we revealed the substrate recognition and anomer-retaining hydrolytic reaction mechanisms of the α- and β-D-arabinofuranosidic bonds in endo- and exo-mode reactions.