|Family type peptidase||N06.001 - YscU protein (Yersinia pseudotuberculosis), MEROPS Accession MER0123660 (peptidase unit: 1-354)|
|Content of family||Family N6 includes autoprocessing endopeptidases.|
Identifier created: MEROPS 9.3 (7 September 2010)|
Pathogenic and symbiotic Gram-negative bacteria can influence some host cells to their advantage by secreting proteins into the host cell cytoplasm. These proteins do not have signal peptides and are secreted by a special mechanism known as the type III secretion system or injectisome. The secretion is mediated by a structure similar to a flagellum, with a basal body and a multimeric filamentous protein structure which protrudes from the bacterial surface and forms a pore in the host cell membrane. The basal body sits in the bacterial cell membrane but opens to the cytoplasm, allowing unfolded proteins to pass along the hollow filament. The FlhB transmembrane protein (N06.002) and its homologues are important when secretion changes from one protein to another (Edqvist et al., 2003). This protein undergoes autoproteloysis at an AsnPro-Thr-His motif (Bjornfot et al. 2009). In Yersinia there are about eleven of these Yersinia Outer membrane Proteins (YOPS), some of which are peptidases in families C55 and C58.
|Active site residues||N263 |
|Active site||Cleavage occurs within the well conserved tetrapeptide AsnPro-Thr-His. In the crystal structure, this tetrapeptide forms a type II beta-turn that is strained, and thus facilitates formation of a hydrogen bond between the carbonyl oxygen of Asn263 and the backbone amide of His266. It is thought that the side chain amide of Asn263 becomes activated and attacks and cleaves the Asn-Pro bond. Cyclization of Asn263 occurs forming a succinamide intermediate which is subsequently hydrolysed (Zarivach et al., 2008). Zarivach et al., 2008 suggest that this cleavage is intein-like.|
|Molecular structure||The EscU protein has two domains, an N-terminal domain involved in the association with the type III secretion system inner membrane basal ring, and a C-terminal domain where cleavage occurs. Tertiary structures have been determined for the C-terminal domain from several homologous proteins, notably EscU from Escherichia coli and SpaS from Salmonella typhimurium (Zarivach et al., 2008). Each structure shows a four-strand beta sheet surrounded by four helices, which is unique to this family. The structure of EscU is the type structure for clan NB.|