Ubiquitin is a regulatory protein found in all eukaryotic organisms that marks proteins for destruction or editing. It employs three enzymes to label proteins and attract more ubiquitin molecules to the scene. Ubiquitin has a wide variety of functions within a cell’s proteins and is believed to play a role in nearly every cellular process. It is used as a disease marker and is associated with genetic diseases such as 3M syndrome, Liddle syndrome, and Angelman syndrome. Ubiquitin and its ubiquitin ligase E3 also bind to a particular protein in a cell, which produces a DNA repair of the protein and allows it to recover its viability.
First identified in 1975, ubiquitin (Ub) is found as an isolated protein in veal sweetbreads and was thought to have something to do with white blood cell maturation. Later found in all tissues of eukaryotic organisms of many species, it was given the name ubiquitin, which comes from the Latin word for “everywhere”. It is a regulatory protein responsible for protein recycling that carries out its responsibilities by binding to proteins and marking them for destruction. This tag targets the tagged proteins to the proteasome complex which degrades and recycles them, or the tag can target other proteins for editing, deoxyribonucleic acid (DNA) repair, or gene transcription. It is considered the most conservative of all proteins because its 76 amino acid sequence differs slightly among all species, whether plant, animal or human.
The process by which this protein labels proteins employs three enzymes: E1, which activates Ub and puts it in a reactive state, E2, which then catalyzes the adhesion of Ub to proteins, and E3, a ubiquitin-ligase that identifies the protein. In this enzyme cascade, Ub is then able to dispel the protein’s protections against proteasomes, so that the proteasome can rapidly degrade and destroy it. Accumulations of aberrant proteins within a cell often result from DNA mutations or mistranslations of genes. Because these aberrant proteins can wreak havoc on a cell’s functions, this chaos is believed to be the underlying malaise that leads to diseases such as Alzheimer’s, Huntington’s, and Parkinson’s. Making use of proteasome-mediated degradation is one of the ways a cell can achieve repair and expulsion of aberrant proteins.
When ubiquitin binds to a protein, it can also attract more ubiquitin molecules to the scene to attack. These interact with it and sometimes perform modifications such as the destruction of sperm cells after fertilization, regulating degradation until destruction, or antigen processing and DNA transcription and repair. It has such a wide variety of functions within a cell’s proteins that it has led some to believe that it plays a role in nearly every cellular process. There are also many Ubiquitin-Like Proteins (UBL) that have divergent roles in cell modification. One is an interferon-stimulating gene modifier, another is a neuronal cell downregulator, and yet another deals with F-antigens in human leukocytes.
Histology departments can use antibodies against this substance to identify cells with abnormal accumulations of aberrant proteins in the cells and use these antibodies as disease markers. Research has developed this use of the antigen to detect Alzheimer’s-associated neurofibrillary tangles, inclusions in motor neuron disease, and mallory bodies in alcoholic liver disease. There are some genetic diseases associated with ubiquitin. One is a mutation of an E3 ubiquitin ligase that leads to an autosomal recessive growth retardation called 3M syndrome. Another is a misregulation and disruption of a gene in Liddle syndrome, which causes high blood pressure. A disruption in the gene is also thought to be the cause of Angelman syndrome, again attributable to dysfunction of the E3 ubiquitin ligase.
Nearly 50% of all cancerous tumors have been found to be deficient in a particular protein that has been dubbed the ‘guardian of the genome’. As long as cells can produce this particular gene, cancer cannot develop in a cell. Ubiquitin and its ubiquitin ligase E3 binds to this particular protein in a cell and this binding produces a DNA repair of the protein and allows it to recover its viability. The ubiquitin-proteasome system also reduces the size of viral proteins for destruction to help the body’s immune system. Just in May 2011, it was announced at the 102nd Convention of the American Association for Research on Cancer that the protein’s enzymatic processes were linked to help the body not reject chemotherapies in non-small cell lung cancers.
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