Family A25


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family A25

NamePeptidase family A25 (gpr protease family)
Family type peptidaseA25.001 - gpr peptidase (Bacillus megaterium), MEROPS Accession MER0001292 (peptidase unit: 17-371)
Content of familyPeptidase family A25 contains a single endopeptidase.
History Identifier created: MEROPS 5.61 (29 October 2001)
During the germination of spores of Bacillus species, 10 - 20% of the proteins ('small acid-soluble proteins': SASP) are degraded in a process that is initiated by the 'germination protease' (A25.001), the product of the gpr gene (Setlow, 1976). The gene was cloned by Sussman & Setlow (1991).
Catalytic typeAspartic
Active site residuesD128 D194 H,K224 
Active siteIt has been shown that Asp128 and Asp194 (see the Alignment) are the only residues essential to the catalytic activitities of gpr peptidase. Mutation of either of these caused loss of both autolytic processing of the proenzyme and substrate cleavage (Carroll & Setlow, 2005). Lys224, which is closely associated with the aspartates in the structure, is less strictly conserved in the family, and is not essential for activity (Carroll & Setlow, 2005).
Activities and specificitiesThe gpr proenzyme (P46) is autolytically processed to the active form (P41: Illades-Aguiar & Setlow, 1994). The main substrates of the mature gpr peptidase are the SASPs that are degraded during spore germination (Setlow, 1988). The peptidase prefers an acidic residue at P1, hydrophobic at P1", Ala at P2" and an acidic residue at P4" (Setlow, 2004).
InhibitorsInhibition of gpr peptidase was investigated by Nessi et al. (1998), who found no significant inhibition by DFP, N-ethylmaleimide, iodoacetamide or pepstatin, or by the metal chelators EDTA, 1,10-phenanthroline and 8-hydroxyquinoline-5-sulfonic acid. Inhibition by 10 mM PMSF that had been reported previously was confirmed, but PMSF did not prevent the autolysis of the gpr proenzyme.
Molecular structureThe gpr peptidase is active as a homotetramer (Loshon & Setlow, 1982). The structure of a truncated form of the proenzyme shows that each monomer consists of two domains: the core domain and the cap domain (Ponnuraj et al., 2000). The core domain contains an 8-stranded beta-sheet with two alpha helices stacked against the beta-sheet and forming a channel. The cap domain contains three helices. The structure of the proenzyme shows no bound metal ion, and chemical analysis of the active enzyme did not reveal the presence of significant quantities of Cd2+, Co2+, Cu2+, Fe2+, Mg2+, Mn2+ or Zn2+ (Nessi et al., 1998). Pei & Grishin (2002) pointed out clan-level homology with the hydrogenase-processing peptidases in family A31.
Basis of clan assignmentProtein fold of the peptidase unit for members of this family resembles that of HybD endopeptidase, the type example of clan AG.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functionsThe gpr proenzyme is synthesised during bacterial sporulation, as are its SASP substrates. At the beginning of the germination process in Bacillus species, the SASPs are degraded by gpr into oligopeptides that are further degraded to amino acids by other peptidases, giving a plentiful supply of amino acids for new protein synthesis in the germinating spore (Setlow, 2004).
ReviewsThe gpr peptidase has been reviewed by Setlow (2004) and Carroll & Setlow (2005).
Statistics for family A25Sequences:323
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
gpr peptidaseA25.001Yes
family A25 non-peptidase homologuesnon-peptidase homologue-
family A25 unassigned peptidasesunassigned-