Family S48

Family

Summary Holotypes Alignment Tree Genomes Structure Literature Architecture

Summary for family S48

Family type peptidase	S48.001 - HetR putative peptidase (Anabaena variabilis), MEROPS Accession MER0004427 (peptidase unit: 1-299)
Content of family	Peptidase 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 type	Serine
Active site residues	S152
Active site	There 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 specificities	HetR 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.
Inhibitors	It is reported that both dansyl fluoride and PMSF can prevent the autolytic activity of HetR (Zhou et al., 1998; Dong et al., 2000).
Molecular structure	HetR is a protein of about 299 amino acids. It has been crystallised (Zhou et al., 1998), but no structure has been reported.
Clan	unassigned
Basis of clan assignment	Protein 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 functions	HetR 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 S48	Sequences:	88
	Identifiers:	1
	Identifiers with PDB entries:	1
Downloadable files	Sequence library (FastA format)
	Sequence alignment (FastA format)
	Phylogenetic tree (Newick format)

Other databases	INTERPRO	IPR005319
	PFAM	PF03574

Peptidases and Homologues	MEROPS ID	Structure
HetR putative peptidase	S48.001	Yes
Family S48 unassigned peptidases	unassigned	-