The endogenous galactofuranosidase GlfH1 hydrolyzes mycobacterial arabinogalactan

Despite the impressive progress made over the past 20 years in our understanding of mycolylarabinogalactan-peptidoglycan (mAGP) biogenesis, the mechanisms by which the tubercle bacillus Mycobacterium tuberculosis adapts its cell wall structure and /composition in response to various environmental conditions, especially during infection, remain poorly understood. Being the central portion of the mAGP complex, arabinogalactan (AG) is believed to be the constituent of the mycobacterial cell envelope that undergoes the least structural changes in its structure, but no reports exist supportings this assumption. Herein, using [MS2] recombinantly expressed mycobacterial protein, bioinformatics analyses, and kinetic and biochemical assays, we demonstrate that the AG can be remodeled by a mycobacterial endogenous enzyme. In particular, we identified found that the mycobacterial protein GlfH1 (Rv3096), which protein exhibits an exo-beta-D-galactofuranose hydrolase activity and is capable of hydrolyzing the galactan chain of AG by recurrent cleavage of the terminal beta-(1,5) and beta-(1,6)-Galf linkages. The characterization of this galactosidase represents the a first step towards understanding the remodeling of mycobacterial AG.