In molecular biology, the HECT domain is a protein domain

Protein domain

A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...

 found in ubiquitin-protein ligases. The name HECT comes from 'Homologous to the E6-AP Carboxyl Terminus'. Protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s containing this domain at the C terminus include ubiquitin-protein ligase, which regulates ubiquitination of . Ubiquitin-protein ligase accepts ubiquitin

Ubiquitin

Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. Among other functions, it directs protein recycling.Ubiquitin can be attached to proteins and label them for destruction...

 from an E2 ubiquitin-conjugating enzyme

Ubiquitin-conjugating enzyme

Ubiquitin-conjugating enzymes, also known as E2 enzymes and more rarely as ubiquitin-carrier enzymes, perform the second step in the ubiquitination reaction that targets a protein for degradation via the proteasome.The ubiquitination process covalently attaches ubiquitin, a short protein of 76...

 in the form of a thioester

Thioester

Thioesters are compounds with the functional group C-S-CO-C. They are the product of esterification between a carboxylic acid and a thiol. Thioesters are widespread in biochemistry, the best-known derivative being acetyl-CoA.-Synthesis:...

, and then directly transfers the ubiquitin to targeted substrates

Substrate (biochemistry)

In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...

. A cysteine

Cysteine

Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

 residue is required for ubiquitin-thiolester formation. Human thyroid receptor interacting protein 12 (TRIP12

TRIP12

Probable E3 ubiquitin-protein ligase TRIP12 is an enzyme that in humans is encoded by the TRIP12 gene.-Further reading:...

), which also contains this domain, is a component of an ATP

Adenosine triphosphate

Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

-dependent multisubunit protein that interact

Protein-protein interaction

Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

s with the ligand binding domain of the thyroid hormone receptor

Thyroid hormone receptor

The thyroid hormone receptor is a type of nuclear receptor that is activated by binding thyroid hormone.-Function:Amongst the most important functions of thyroid hormone receptors are regulation of metabolism and heart rate...

. It could be an E3 ubiquitin-protein ligase. Human ubiquitin-protein ligase E3A

UBE3A

Ubiquitin-protein ligase E3A also known as E6AP ubiquitin-protein ligase is an enzyme that in humans is encoded by the UBE3A gene. This enzyme is involved in targeting proteins for degradation within cells...

 interact

Protein-protein interaction

Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

s with the E6 protein of the cancer-associated Human papillomavirus

Human papillomavirus

Human papillomavirus is a member of the papillomavirus family of viruses that is capable of infecting humans. Like all papillomaviruses, HPVs establish productive infections only in keratinocytes of the skin or mucous membranes...

 type 16 and Human papillomavirus type 18. The E6/E6-AP complex

Protein complex

A multiprotein complex is a group of two or more associated polypeptide chains. If the different polypeptide chains contain different protein domain, the resulting multiprotein complex can have multiple catalytic functions...

 binds to and targets the P53

P53

p53 , is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer...

 tumour-suppressor protein for ubiquitin-mediated proteolysis

Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...

.