Family S51


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family S51

Family type peptidaseS51.001 - dipeptidase E (Escherichia coli), MEROPS Accession MER0001335 (peptidase unit: 1-229)
Content of familyPeptidase family S51 contains exopeptidases that hydrolyse alpha-aspartyl bonds.
History Identifier created: Methods Enzymol. 248:105-120 (1995)
A study of peptidases that hydrolyse Asp-Xaa dipeptides led to the discovery of alpha-aspartyl dipeptidase (S51.001) (Carter & Miller, 1984). Homologues include one from Xenopus with activity similar to the bacterial enzyme (S51.002), and cyanophycinase from cyanobacteria (S51.003). There are unrelated aspartyl dipeptidases that hydrolyse bonds formed by the side chain or beta-carboxyl group of aspartate, not alpha-aspartyl bonds; these are beta-aspartyl dipeptidase (M38.001) and isoaspartyl peptidase (T02.002).
Catalytic typeSerine
Active site residuesS120 H157 E192 
Active siteSite directed mutagenesis and the three-dimensional structure of alpha-aspartyl dipeptidase show a catalytic triad: Ser120, His157 and Glu192 (see the Alignment). Asp135 is essential for activity (Lassy & Miller, 2000), although it is now known not to be a member of the catalytic triad.
Activities and specificitiesalpha-Aspartyl dipeptidase hydrolyses Asp-Xaa dipeptides in which Xaa is not Glu, Asn or Gln. Asp-Gly-Gly is the only substrate larger than a dipeptide that is hydrolysed. The alpha-carboxyl group of the dipeptide is not required, and Asp-NHPhNO2 is a good test substrate (Lassy & Miller, 2000). Cyanophycinase acts on cyanophycin, an unusual storage polymer that has a poly-alpha-aspartate backbone. Each of the side chain beta-carboxyl groups of cyanophycin forms an isopeptide link to the alpha-amino group of an arginine residue. Cyanophycin attacks the polymer as an exopeptidase (probably from the N-terminus), releasing the beta-Asp-Arg dipeptide, which it is not able to cleave (Richter et al., 1999).
InhibitorsDespite being a serine peptidase, alpha-aspartyl dipeptidase is not inhibited by DFP or PMSF (Carter & Miller, 1984).
Molecular structureThe three-dimensional structure of alpha-aspartyl dipeptidase reveals a class I glutamine amidotransferase-like fold. This links family S51 to families C26 and C56 in clan PC.
Basis of clan assignmentType family of clan PC.
Distribution of family Bacteria details  
Archaea details  
Protozoa details  
Fungi -  
Plants details  
Animals details  
Viruses -  
Biological functionsThe known functions of the peptidases in family S51 are nutritional: alpha-aspartyl dipeptidase helps Salmonella typhimurium to use aspartyl dipeptides as food sources, and cyanophycinase mobilises the nitrogen-rich polymer stored by some cyanobacteria.
ReviewsReviews that are particularly recommended are those of Miller (2004) for alpha-aspartyl dipeptidase and Richter et al. (1999) for cyanophycinase.
Statistics for family S51Sequences:2560
Identifiers with PDB entries:3
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Other databases INTERPRO IPR005320
PFAM PF03575
SCOP 52331
Peptidases and Homologues MEROPS ID Structure
dipeptidase ES51.001Yes
alpha-aspartyl dipeptidase (eukaryote)S51.002-
family S51 non-peptidase homologuesnon-peptidase homologueYes
family S51 unassigned peptidasesunassigned-