|Family type peptidase||S53.001 - sedolisin (Pseudomonas sp. 101), MEROPS Accession MER0000995 (peptidase unit: 216-585)|
|Content of family||Peptidase family S53 contains acid-acting endopeptidases and a tripeptidyl-peptidase.|
Identifier created: MEROPS 5.3 (4 December 2000)|
Endopeptidases with acidic pH optima that differ from the majority of such enzymes in being resistant to inhibition by pepstatin were discovered by Murao, Oda and co-workers in the early 1980s (e.g. Terashita et al., 1981; Oda et al., 1998). Crystal structures have shown that many of these pepstatin-insensitive carboxyl proteinases are either glutamic peptidases in family G1 or sedolisins in family S53, both groups being unrelated to the aspartic peptidases of clan AA that are inhibited by pepstatin.
|Active site residues||E295 D299 D385 S502 |
|Active site||The residues of the catalytic triad are Glu, Asp, Ser, and there is an additional acidic residue, Asp385 (numbering as in the Alignment) in the oxyanion hole (Wlodawer et al., 2003). The Ser residue is the nucleophile equivalent to Ser in the Asp, His, Ser triad of subtilisin, and the Glu of the triad is a substitution for the His general base in subtilisin. The residue that orients the general base side chain is quite different between the families, however, being Asp299 in family S53 (closely following Glu295 in the sequence), in contrast to Asp137 preceding His in the sequence of subtilisin. Asp385 of the oxyanion hole corresponds to Asn259 in subtilisin.|
|Activities and specificities||The specificities of sedolisin (S53.001) and sedolisin-B (S53.002) have been described by Narutaki et al. (1999) and Wlodawer et al. (2001). The specificities are broad, but there is an indication of preferences for hydrophobic residues in the P1 and P2 positions. |
Having predominantly (though not exclusively) exopeptidase activity, tripeptidyl-peptidase I (S53.003) differs from the sedolisins. The structural basis of the specificity has been discussed by Wlodawer et al. (2003). Ala-Arg-PheNph-Arg-Leu has been described as a particularly sensitive substrate, with a specificity constant 40-fold that of Ala-Ala-PheNHMec, the substrate generally used for the enzyme (Wlodawer et al., 2001).
The peptidases of the sedolisin family tend to be most active at acidic pH (unlike the homologous subtilisins), and this can be attributed to the functional importance of carboxylic residues, notably Asp385 in the oxyanion hole.
|Inhibitors||Most known inhibitors are aldehydes containing large hydrophobic side chains, such as tyrostatin and chymostatin. These make covalent bonds to the active site Ser502 (numbering as in the Alignment) through their aldehyde moieties (Wlodawer et al., 2001).|
|Molecular structure||High-resolution structures have been published for sedolisin (Wlodawer et al., 2001), kumamolisin (Comellas-Bigler et al., 2002), kumamolisin As (S53.009: Wlodawer et al., 2004) and prokumamolisin (Comellas-Bigler et al., 2004). The protein folds are clearly related to that of subtilisin (S08.001), but there are additional loops. The amino acid sequences are not closely similar to those in family S8, and this, taken together with the quite different active site residues and the resulting lower pH for maximal activity, justifies the separate families. However, it should be noted that some other databases choose to combine our families S8 and S53 in a single family.|
|Basis of clan assignment||Protein fold of the peptidase unit for members of this family resembles that of subtilisin, the type example of clan SB.|