Mechanism of <i>O</i>-Glycan Core Structure Degradation by a Mucin-Utilizing <i>Bifidobacterium</i>

The degradation of mucin glycans by gut bacteria is closely associated with the onset and progression of intestinal diseases and is related to symbiotic intestinal colonization by the gut microbiota and mucosal homeostasis. Based on the analyses of enzymes derived from Bifidobacterium bifidum, a mucin O-glycan-utilizing bacterium, we elucidated the degradation pathways of the four major core structures of mucin O-glycans. β- N-Acetylglucosaminidases BbhI and BbhIV and a sulfoglycosidase BbhII act cooperatively to degrade the core structures into core 1 (T antigen) and/or Tn antigen. This mini-review describes the mechanisms by which B. bifidum and other gut microbes degrade the core structure of mucin O-glycans.