| Type: | Conserved_site | Name: | Histidine triad, conserved site |
| Description: | The Histidine Triad (HIT) motif, His-x-His-x-His-x-x (x, a hydrophobic amino acid) was identified as being highly conserved in a variety of organisms []. Crystal structure of rabbit Hint, purified as an adenosine and AMP-binding protein, showed that proteins in the HITsuperfamily are conserved as nucleotide-binding proteins and that Hint homologues, which are found in all forms of life, are structurally related to Fhit homologues and GalT-related enzymes, which have more restricted phylogenetic profiles []. Hint homologues including rabbit Hint and yeastHnt1 hydrolyse adenosine 5' monophosphoramide substrates such as AMP-NH2 and AMP-lysine to AMP plus the amine product and function as positive regulatorsof Cdk7/Kin28 in vivo []. Fhit homologues are diadenosine polyphosphate hydrolases [] and function as tumour suppressors in human and mouse [] though the tumour suppressing function of Fhit does not depend on ApppA hydrolysis []. The third branch of the HIT superfamily, which includesGalT homologues, contains a related His-X-His-X-Gln motif and transfers nucleoside monophosphate moieties to phosphorylated second substrates ratherthan hydrolysing them [].The bovine protein kinase C inhibitor, PKCI-1, is an inhibitor protein that binds zinc without the use of zinc-finger motifs []. Each protein molecule binds one zinc ion via a novel binding site containing 3 closely-spaced histidine residues []. This region, referred to as the histidine triad (HIT) [], has been identified in various prokaryotic and eukaryotic proteins of uncertain function [].The signature pattern used in this entry contains the region of the histidine triad and includes the three conserved histidine residues which are thought to bind the zinc ion. | Short Name: | Histidine_triad_CS |
