Family S48


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family S48

Family type peptidaseS48.001 - HetR putative peptidase (Anabaena variabilis), MEROPS Accession MER0004427 (peptidase unit: 1-299)
Content of familyPeptidase family S48 contains the protein HetR that is reported to be an autolytic serine endopeptidase.
History Identifier created: MEROPS 5.00 (20 April 2000)
A mutant strain of the cyanobacterium Anabaena 7120 was found to be defective in heterocyst formation, and the defect was traced to a Ser179Asn mutation in the protein HetR (Buikema & Haselkorn, 1991). It was subsequently found that recombinant HetR degrades spontaneously in vitro, but the Ser179Asn mutant protein does not (Zhou et al., 1998). This led to the conclusion that HetR is an unusual serine peptidase.
Catalytic typeSerine
Active site residuesS152 
Active siteThere is evidence that two conserved Ser residues are required for the self-cleaving activity of HetR. As has been mentioned, the self-cleaving activity of HetR was not present in the Ser179Asn mutant (Zhou et al., 1998). Similarly, the Ser152Ala mutant also lacked the auto-proteolytic activity (Dong et al., 2000). It should be mentioned that in these studies, dansyl fluoride was used as if it is a specific inhibitor of serine peptidases, which is not the case. The better reagent, PmsF, was used in some experiments.
Activities and specificitiesHetR itself is the only reported substrate of the peptidase activity of HetR. Activity was seen at pH 7.5, only in the presence of 1 mM CaCl2 (Zhou et al., 1998). The fragmentation obtained was indicative of cleavage of at least three bonds, but the bonds were not identified. If HetR can cleave itself in three positions, it can probably cleave other substrates too.
InhibitorsIt is reported that both dansyl fluoride and PMSF can prevent the autolytic activity of HetR (Zhou et al., 1998; Dong et al., 2000).
Molecular structureHetR is a protein of about 299 amino acids. It has been crystallised (Zhou et al., 1998), but no structure has been reported.
Basis of clan assignmentProtein fold and active site residues (except the catalytic serine) are not known for any members of this family.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functionsHetR plays an essential role in the differentiation of heterocysts in Anabeana (Khudyakov & Golden, 2004), and mutations that prevent the cleavage of the protein also inactivate its function in differentiation.
Statistics for family S48Sequences:88
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
HetR putative peptidaseS48.001Yes
family S48 unassigned peptidasesunassigned-