This is the catalytic helper subdomain found in collagenase G from Clostridium histolyticum. This domain is indispensable for proper folding and full peptidase activity [1, 2].

1: Structural basis for activity regulation and substrate preference of clostridial collagenases G, H, and T. Eckhard U, Schonauer E, Brandstetter H; J Biol Chem. 2013;288:20184-20194. PMID:23703618

2: Structure of collagenase G reveals a chew-and-digest mechanism of bacterial collagenolysis. Eckhard U, Schonauer E, Nuss D, Brandstetter H; Nat Struct Mol Biol. 2011;18:1109-1114. PMID:21947205