Family S51
Summary for family S51
| Family type peptidase | S51.001 - dipeptidase E (Escherichia coli), MEROPS Accession MER0001335 (peptidase unit: 1-229) |
| Content of family | Peptidase 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 type | Serine |
| Active site residues | S120 H157 E192 |
| Active site | Site 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 specificities | alpha-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). |
| Inhibitors | Despite being a serine peptidase, alpha-aspartyl dipeptidase is not inhibited by DFP or PMSF (Carter & Miller, 1984). |
| Molecular structure | The 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. |
| Clan | PC |
| Subclan | PC(S) |
| Basis of clan assignment | Type family of clan PC. |
