Flagellinolysin: bacterial flagellar metallopeptidase

Flagellins are polymeric proteins that assemble to form the extracellular filaments of bacterial flagella. Flagellins have a common domain architecture consisting of an N-terminal and C-terminal domains that assemble the core filament and a hypervariable central region that is surface-exposed. Flagellinolysin is a unique variant of bacterial flagellin that possesses a metallopeptidase domain in the hypervariable region, resulting in extracellular localization of proteolytic activity to flagellar filament surfaces. Thus far, flagellinolysins have been identified in almost 300 bacterial species and partially characterized in a gram-negative (Hylemonella gracilis) as well as a gram-positive (Clostridium haemolyticum) organism. Flagellinolysins are HExxH-containing MEROPS M101 metalloproteases with similarities to clostridial collagenases and demonstrate protease activity in the form of recombinantly produced enzymes as well as native preparations of purified flagellar filaments. The biological function of flagellinolysin is still unclear but may involve extracellular proteolysis for nutrition, host cell penetration, virulence, interbacterial interactions, and biofilm development.