Proteolysis refers to the cutting up or digestion of proteins. DPP as originally synthesized is inactive. Undergoing proteolysis allows DPP to become active. Tolloid protein contains a metalloprotease, and is therefore, a candidate for DPP proteolysis. In addition to a protease domain, TLL possesses two epidermal growth factor repeats and five copies of a repeat found in certain vertebrate complement components.
Complement consists of enzymes that kill cells when activated by antibody molecules.
The BMPs were initially identified as a copurifying mixture of proteins capable of inducing ectopic bone formation in rats. As in rats, it is likely that the BMP family members Tolloid and DPP likewise physically interact. Tolloid enhances DPP function, while Short gastrulation , an ortholog of the Xenopus organizer Chordin, inhibits DPP function. Tolloid is secreted and requires a protelytic processing step for activation. The removal of the N-terminal prodomain is not catalyzed by TLD itself, since it is removed from a putative TLD protease null mutant.