Family N4


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family N4

Family type peptidaseN04.001 - Tsh-associated self-cleaving domain (Escherichia coli) and similar (Escherichia coli), MEROPS Accession MER0187148 (peptidase unit: 1100-1377)
Content of family
History Identifier created: MEROPS 9.3 (7 September 2010)
Autotransporters are virulence factors secreted by pathogenic, Gram-negative bacteria, an example being Tsh (S06.003) which is a peptidase secreted by Escherichia coli. It is synthesized as a precursor with a signal peptide and a large C-terminal propeptide (Stathopoulos et al., 1999). The C-terminal propeptide forms a pore in the outer membrane through which the peptidase domain can pass. Autolytic cleavage then occurs at Asn1100, releasing the peptidase. The mature peptidase is known as the 'passenger' domain.
Catalytic typeAsparagine
Active site residuesN1100 Y1227 E1249 R1282 
Active siteThe identification of an unusual catalytic dyad in Escherichia coli EspP protein (S06.002) consisting of Asp1197 and Asn1100 was first made by Dautin et al., 2007, who also showed that autolytic cleavage occurred when Asp1197 was replaced by glutamate. It is believed that Asn1100 acts as the nucleophile during self-cleavage and that cleavage happens in cis. Asparagine is a unique amino acid that can attack the main chain carbonyl bond to create a stable five-membered ring bearing a succinimide that is subsequently hydrolysed by water (Dautin et al., 2007). From the crystal structure of Tsh, other residues are thought to be important: Lys1201 and Tyr1227 form hydrogen bonds with Asn1100 holding it in place while Arg1121 positions the side chain for nucleophilic attack; Glu1249 assists nucleophilic attack by protonating the carbonyl and forms a salt bridge with Arg1282 (Tajima et al., 2010). The catalytic mechanism has been likened to that of inteins (Tajima et al., 2010).
Activities and specificitiesThe only peptidase activity is release of the passenger domain from the precursor.
Molecular structureThe tertiary structure of the C-terminal propeptide has been solved, and shows a 12-stranded beta barrel domain unlike that of any other peptidase (Tajima et al., 2010). There is uncertainty about which residues constitute the peptidase domain; at present the peptidase domain is defined as the C-terminal propeptide plus the nucleophilic asparagine. The C-terminal propeptide is the type structure for clan ND.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals details  
Viruses details  
Biological functionsThe autolytic cleavage causes the virulence factor to be secreted.
Statistics for family N4Sequences:456
Identifiers with PDB entries:3
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
Tsh-associated self-cleaving domain (Escherichia coli) and similarN04.001Yes
EspP gamma protein autotransporter domain (Escherichi-type)N04.002Yes
family N4 non-lyase homologuesnon-peptidase homologueYes
family N4 unassigned peptide lyasesunassigned-