This domain is found in the proenzyme form of Vacuolar-processing enzyme (VPE), known as legumain. VPE is an asparagine-specific endopeptidase that plays important roles in many physiological processes, including the maturation of toll-like receptors 3/7/9. The mature active form of VPE is generated by autoproteolytic maturation at acidic pH. In the three-dimensional structure of the proenzyme, this prodomain is located on top of the protease domain, blocking access to the active site. It shows an entirely alpha-helical fold, with an activation peptide and a region that assemblies into a death domain-like fold at its C-terminal end [1-5].

1: Mechanistic and structural studies on legumain explain its zymogenicity, distinct activation pathways, and regulation. Dall E, Brandstetter H; Proc Natl Acad Sci U S A. 2013;110:10940-10945. PMID:23776206

2: Structural analysis of asparaginyl endopeptidase reveals the activation mechanism and a reversible intermediate maturation stage. Zhao L, Hua T, Crowley C, Ru H, Ni X, Shaw N, Jiao L, Ding W, Qu L, Hung LW, Huang W, Liu L, Ye K, Ouyang S, Cheng G, Liu ZJ; Cell Res. 2014;24:344-358. PMID:24407422

3: Engineering a Catalytically Efficient Recombinant Protein Ligase. Yang R, Wong YH, Nguyen GKT, Tam JP, Lescar J, Wu B; J Am Chem Soc. 2017;139:5351-5358. PMID:28199119

4: Crystal Structure of Plant Legumain Reveals a Unique Two-Chain State with pH-Dependent Activity Regulation. Zauner FB, Dall E, Regl C, Grassi L, Huber CG, Cabrele C, Brandstetter H; Plant Cell. 2018;30:686-699. PMID:29453229

5: Structural basis of ribosomal peptide macrocyclization in plants. Haywood J, Schmidberger JW, James AM, Nonis SG, Sukhoverkov KV, Elias M, Bond CS, Mylne JS; Elife. 2018; [Epub ahead of print] PMID:29384475