Family C13


Summary Holotypes Alignment Tree Genomes Structure Literature H-seq M-seq

Summary for family C13

NamePeptidase family C13 (legumain family)
Family type peptidaseC13.001 - legumain (plant beta form) (Canavalia ensiformis), MEROPS Accession MER0000845 (peptidase unit: 36-312)
Content of familyPeptidase family C13 contains asparaginyl endopeptidases and glycosylphosphatidylinositol:protein transamidase.
History Identifier created: Biochem.J. 290:205-218 (1993)
An asparginyl endopeptidase was first discovered in beans, and the sequencing of homologues from the blood fluke Schistosoma mansoni led to the discovery of expressed sequence tags from humans and the completion of the first mammalian sequence (Chen et al., 1997). Mammalian legumain (C13.004) was localized to the lysosome, an organelle already known to be rich in peptidases. A second mammalian enzyme, glycosylphosphatidylinositol:protein transamidase (C13.005), has been discovered.
Catalytic typeCysteine
Active site residuesH158 C200 
Active siteThe active site residues are in the order His, Cys in the protein sequence. The histidine occurs within the motif Xaa-Xaa-Xaa-Xbb-Xbb-His-Gly-Xbb, in which Xaa is a hydrophobic amino acid and Xbb is a small amino acid (Ala, Asp, Glu, Gly, Ser or Thr). The cysteine occurs in a similar motif, Xaa-Xaa-Xaa-Xbb-Xbb-Cys. From structural studies, a catalytic triad (Asn, His, Cys) has been proposed (Dall & Brandstetter, 2013 ) but there are no studies to show the asparagine is essential.
Activities and specificitiesMost members of the family are endopeptidases with a restricted specificity for asparaginyl bonds, although only a minority of such bonds are cleaved in proteins (Dando et al., 1999). One of the best synthetic substrates for mammalian legumain is Z-Ala-Ala-Asn-NHMec. Maximal activity is seen at pH 4-6; at higher pH legumain is denatured. At pH 4.0, cleavage at aspartyl bonds has been observed. The strict specificity for the P1 residue of the substrate is a characteristic shown also by other peptidases in clan CD.
InhibitorsPeptidases in family C13 are inhibited by thiol-blocking reagents such as iodoacetamide and N-ethylmaleimide, but are unaffected by E-64 and leupeptin, potent inhibitors of peptidases in family C1. Members of family C13 react more rapidly with iodoacetamide than with iodoacetate, the reverse of what is found for peptidases in family C1. Aza-peptide epoxides are also potent inhibitors of legumains (James et al., 2003). Like many peptidases in family C1, legumain is inhibited by ovocystatin (I25.001), but by a different reactive site (Alvarez-Fernandez et al., 1999).
Molecular structureIn keeping with its lysosomal location, mammalian legumain is glycosylated. Some plant legumains also are glycosylated, although not that of castor bean. No tertiary structure has been reported, but similarities in sequence and predicted secondary structure around the active site residues lead Chen et al., (1998) to assign family C13 to clan CD, and to suggest that the fold is similar to that of the caspases in family C14.
Basis of clan assignmentActive site residues for members of this family and family C14 occur in the same order in the sequence: H, C.
Distribution of family Bacteria details  
Archaea details  
Protozoa details  
Fungi details  
Plants details  
Animals details  
Viruses -  
Biological functionsLegumain is synthesized as a precursor with both N- and C-terminal propeptides. Prolegumain is directed to the lysosome or plant vacuole, where activation occurs at least partially by autolysis (Chen et al., 2000). Human legumain has been shown to process the tetanus toxin generating the fragments found in class II antigen presentation (Manoury et al., 1998). Legumain from plant seeds is thought to be responsible for the post-translational processing of seed proteins prior to storage (Hara-Nishimura et al., 1995). Glycosylphosphatidylinositol:protein transamidase is found in the endoplasmic reticulum, where it removes a C-terminal peptide from a susceptible protein and attaches a glycosylphosphatidylinositol moiety by a transamidase reaction that anchors the substrate protein to the membrane.
ReviewsChen et al. (2004)
Statistics for family C13Sequences:2151
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
legumain (plant beta form)C13.001-
legumain (plant alpha form)C13.002-
legumain, animal-typeC13.004Yes
glycosylphosphatidylinositol:protein transamidaseC13.005-
legumain (plant gamma form)C13.006-
legumain, trematode-typeC13.007-
legumain, Blastocystis-typeC13.008-
butelase 1C13.009-
legumain (plant delta form)C13.A01-
T28H10.3 (Caenorhabditis elegans)C13.A02-
DKEY-157L19.1-001 g.p. (Brachydanio rerio)C13.A03-
legumain pseudogene (Homo sapiens)C13.P01-
family C13 non-peptidase homologuesnon-peptidase homologue-
family C13 unassigned peptidasesunassigned-