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DHHC domain
In molecular biology the DHHC domain is a protein domain that acts as an enzyme, which adds a palmitoyl chemical group to proteins in order to anchor them to cell membranes. The DHHC domain was discovered in 1999 and named after a conserved sequence motif found in its protein sequence. Roth and colleagues showed that the yeast Akr1p protein could palmitoylate Yck2p ''in vitro'' and inferred that the DHHC domain defined a large family of palmitoyltransferases. In mammals twenty three members of this family have been identified and their substrate specificities investigated. Some members of the family such as ZDHHC3 and ZDHHC7 enhance palmitoylation of proteins such as PSD-95, SNAP-25, GAP43, Gαs. Others such as ZDHHC9 showed specificity only toward the H-Ras protein.〔 However, a recent study questions the involvement of classical enzyme-substrate recognition and specificity in the palmitoylation reaction. Several members of the family have been implicated in human diseases.
==Sequence motifs==
Conserved motifs within protein sequences point towards the most important amino acid residues for function. In the DHHC domain there is a tetrapeptide motif composed of aspartate-histidine-histidine-cysteine. However this short sequence is embedded in a larger region of about fifty amino acids in length that shares many more conserved amino acids. The canonical DHHC domain can be described with the following sequence motif:
'' C-x2-C-x9-HC-x2-C-x4-DHHC-x5-C-x4-N-x3-F'' (x shows region of unconserved residues)
However many examples of DHHC domains are known that do not contain all these conserved residues. In addition to the central DHHC domain three further sequence motifs have been identified in members of the DHHC family. A ''DPG'' (aspartate-proline-glycine) motif has been identified just to the C-terminus of the second transmembrane region. A ''TTxE'' (threonine-threonine-any-glutamate) motif has also been identified after the fourth transmembrane helix.〔 A third motif towards the C-terminus of many proteins has been identified that contains a conserved aromatic amino acid, a glycine and an asparagine called the PaCCT motif (PAlmitoiltransferase Conserved C-Terminus motif).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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