Family C44


Summary Holotypes Alignment Tree Genomes Structure Literature H-seq M-seq

Summary for family C44

Family type peptidaseC44.001 - amidophosphoribosyltransferase precursor (Homo sapiens), MEROPS Accession MER0003314 (peptidase unit: 12-277)
Content of familyPeptidase family C44 contains the self-processing precursor of amidophosphoribosyltransferase.
History Identifier created: MEROPS 5.00 (20 April 2000)
Amidophosphoribosyltransferase (EC is synthesised with an 11-residue, N-terminal propeptide that is cleaved off autolytically. Only the precursor form of the enzyme can be regarded as a peptidase, since there is no indication that the mature enzyme hydrolyses peptide bonds, although Cys12, the nucleophile in cleavage of the propeptide, becomes the N-terminal active site residue in the amidotransferase reaction catalysed by the mature enzyme. There are several homologues of amidophosphoribosyltransferase that are synthesised in the active form, i.e. Cys1 has the amidotransferase activity, requiring only removal of an initiator methionine residue; these are regarded as non-peptidase homologues in family C44.
Catalytic typeCysteine
Active site residuesC12 
Active siteCys12, the N-terminal residue of the peptidase unit (see the Alignment), is the nucleophile in catalysis, analogous to the threonine residues that mediate self-maturation of the subunits of the proteasome in family T1.
Activities and specificitiesThe only known peptidase activity is the autolytic cleavage of the amidophosphoribosyltransferase precursor protein.
Molecular structureOn the basis of the three-dimensional structure of the processed form, amidophosphoribosyltransferase precursor (C44.001) was one of the first N-terminal nucleophile hydrolases to be recognised (Brannigan et al., 1995), and is placed in clan PB(C).
Basis of clan assignmentProtein fold of the peptidase unit for members of this family resembles that of archaean proteasome subunit B, the type example of clan PB.
Distribution of family Bacteria details  
Archaea details  
Protozoa details  
Fungi details  
Plants details  
Animals details  
Viruses details  
Biological functionsEvidently the autolytic processing of the precursor of amidophosphoribosyltransferase makes available the catalytic activity of the transferase, but the function of the latency of the precursor is not understood, since several homologous enzymes with similar kinds of activity are synthesised already in active form.
Statistics for family C44Sequences:11342
Identifiers with PDB entries:7
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
amidophosphoribosyltransferase precursorC44.001Yes
glutamate synthase (NADPH) large chainC44.003Yes
ferredoxin-dependent glutamate synthase 1 (chloroplast, mitochondria)C44.951-
glutamine-fructose-6-phosphate transaminase 1C44.970Yes
glucosamine-fructose-6-phosphate aminotransferaseC44.971Yes
glutamine:fructose-6-phosphate amidotransferaseC44.972-
Mername-AA144 proteinC44.973-
asparagine synthetaseC44.974-
glutamine-fructose-6-phosphate transaminase 2C44.975-
AsnB proteinC44.976Yes
At2g16570 (Arabidopsis thaliana)C44.A01-
At4g38880 (Arabidopsis thaliana)C44.A02-
At4g34740 (Arabidopsis thaliana)C44.A03-
At4g27450 (Arabidopsis thaliana)C44.A04-
glutamine-fructose-6-phosphate transaminase precursor (Dictyostelium discoideum)C44.A08-
PF0204 protein (Pyrococcus furiosus )C44.A09-
family C44 non-peptidase homologuesnon-peptidase homologueYes
family C44 unassigned peptidasesunassignedYes