Family S24
Summary for family S24
| Name | Peptidase family S24 (LexA family) |
|---|
| Family type peptidase | S24.001 - repressor LexA (Escherichia coli), MEROPS Accession MER0000569 (peptidase unit: 85-202) |
| Content of family | Peptidase family S24 contains two-domain proteins that undergo autolysis, separating the functional domains. |
| History |
Identifier created: Methods Enzymol. 244:19-61 (1994)
|
| Catalytic type | Serine |
| Active site residues | S119 K156 |
| Active site | The active site consists of a Ser, Lys catalytic dyad much more widely spaced than in the serine-type D-Ala-D-Ala carboxypeptidases (see clan SE). The nucleophilic hydroxyl group of the serine attacks the si-face of the peptide bond rather than the re-face, which is the usual mode of attack in serine peptidases (Paetzel & Strynadka, 1999). |
| Activities and specificities | The endopeptidases in family S24 perform only one cleavage: autolysis which separates the DNA-binding domain from the rest of the protein. Cleavage occurs at an Ala Gly or a CysGly bond. In repressor LexA (S24.001), cleavage only occurs when LexA associates with the RecA protein. LexA occurs in two conformations, cleavable and non-cleavable. In the cleavable form, a large conformation change occurs placing the cleavage site adjacent to the active site. The non-cleavable state is more stable, but the cleavable form is stabilized by the RecA protein (Luo et al., 2001). |
| Molecular structure | The tertiary structures of several members of the family have now been determined, including the cleaved form of the UmuD protein (S24.003; Peat et al., 1996), and native and cleaved forms of repressor LexA (Luo et al., 2001). The proteins consist mainly of beta structure, in contrast to the serine-type D-Ala-D-Ala carboxypeptidases which are alpha/beta proteins. UmuD exists in solution as a homodimer. |
| Clan | SF |
| Basis of clan assignment | Type family of clan SF. |
| Biological functions | Repressor LexA is involved in the SOS response leading to the repair of single-stranded DNA within the bacterial cell. Single-stranded DNA activates the RecA protein, which in turn mediated LexA cleavage. Cleaved LexA no longer acts as a repressor, which means that several LexA-controlled genes are switched on. These genes are involved in DNA repair and other cell survival processes. UmuD is also involved in the SOS response, but here cleavage releases and activates the DNA polymerase UmuC which forms a complex with uncleaved UmuD (Reuven et al., 1999). Cleavage of the bacteriophage lambda repressor CI leads to prophage induction: the prophage is integrated into the host genome, but expession is blocked by repressor CI until the SOS response leads to CI autolysis, derepression of the prophage and expression of the lytic genes and growth of the virus (Little, 2004). |
| Statistics for family S24 | Sequences: | 14488 |
| Identifiers: | 6 |
| Identifiers with PDB entries: | 4 |
| Downloadable files |
Sequence library (FastA format) |
| Sequence alignment (FastA format) |
| Phylogenetic tree (Newick format) |
