Family M81

Family

Summary Holotypes Alignment Tree Genomes Structure Literature Architecture

Summary for family M81

Family type peptidase	M81.001 - microcystinase MlrC (Sphingomonas sp. ACM-3962), MEROPS Accession MER0167712 (peptidase unit: 1-325)
Content of family	Peptidase family M81 contains metallopeptidases.
History	Identifier created: MEROPS 9.4 (31 January 2011) Microcystins are peptide toxins produced by cyanobacteria which can cause hepatotoxicity by inhibiting protein phosphatases. Microcystins are heptapeptides containing unusual amino acids. Microcystin LR (cyclo(NH2-Adda-isoGlu-methyldehydroAla-Leu-beta-methylAsp-Arg)) is one of the commonest microcystins, persisting in contaminated water supplies for weeks. Efforts to find a method to remove the microcystin led to the discovery of a species of Sphingomonas which can utilize the microcystin as a source of carbon and nitrogen. The bacterium has three specialized peptidase to degrade it. Microcystinase (G05.004) converts the cyclic peptide to a linear peptide, MlrB peptidase (S12.009) cleaves the methyldehydroAla-Leu bond to generate two fragments (Bourne et al., 1996), and the tetrapeptide is further degraded by the MlrC peptidase (M81.001; Bourne et al., 2001) but the exact cleavage position is unknown.
Catalytic type	Metallo
Active site	From the deduced crystal structure of a homologue from Mesorhizobium sp. BNC1, a single zinc ion is bound by Asp38, His140 and His162. The histidines are well conserved, but the aspartic acid is not.
Activities and specificities	The MlrC peptidase from Sphingopyxis degrades both microcystins LR and LA (Ho et al., 2007).
Inhibitors	The MlrC peptidase is assumed to be a metallopeptidase because of inhibition by metal chelators (Bourne et al., 2001).
Molecular structure	The tertiary structure has been solved for a biochemically uncharacterized homologue from Mesorhizobium sp. BNC1. The structure has been deposited in the Protein Data Bank but has not yet been published. The structure show a two-domain protein, with each domain containing a beta sheet surrounded by helices. The active site containing the zinc ion is between the domains. The fold is unlike that of any other peptidase, but related to ABC ribose transporters, alanine racemase, maltose operon transcriptional repressors, and chemotaxis protein Chey. Consequently, the structure of the Mesorhizobium homologue is the type structure for clan MT.
Clan	MT

Distribution of family	Bacteria	details
	Archaea	details
	Protozoa	-
	Fungi	-
	Plants	-
	Animals	details
	Viruses	-

Biological functions	The genes for the three microcystin-degrading peptidases and a putative oligopeptide transporter are found in the same 5.8 kilobase genomic fragment (Bourne et al., 2001).
Statistics for family M81	Sequences:	548
	Identifiers:	1
	Identifiers with PDB entries:	1
Downloadable files	Sequence library (FastA format)
	Sequence alignment (FastA format)
	Phylogenetic tree (Newick format)

Other databases	INTERPRO	IPR015995
	PFAM	PF07171
	PFAM	PF07364

Peptidases and Homologues	MEROPS ID	Structure
microcystinase MlrC	M81.001	-
Family M81 unassigned peptidases	unassigned	Yes