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UBIQUITIN |
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General |
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History… Ubiquitin was discovered accidentally by Joseph Goldstein’s group in the early 70’s, during investigations on biochemical mechanism of myastenia gravis. A new protein was isolated in 1974 from cattle’s thymus as a lymphocyte differentiation promoting factor [3]. This protein is responsible for differentiation of both populations of lymphocytes, T and B ones. This new isolated protein was mistakenly thought to be a thymic hormone then. A year later scientists detected ubiquitin by ubiquitin specified antibodies in many eukaryotic cells. So that was the way of naming this protein “ubiquitin” because it is ubiquitous for different eukaryotic living organisms [3]. Ubiquitin was also found in archaebacteria cells [38]. In 1975 ubiquitin amino acids sequence became known. It was previously supposed to be the protein of 74 amino acid residues, because two C-terminal glycines are very often lost during the ubiquitinylation process [30]. Two years later ubiquitin was found as a part of A24 protein (M.W. = 28451 Da) [4] present in chromatin. The second part of this protein was histone H2A. Ubiquitin is connected with histone by isopeptidic bond between C-terminal glycine of ubiquitin and e-amino group of Lys119 of H2A histone [5]. So this suggested a new role for ubiquitin and established that ubiquitin could be conjugated to other proteins. In the late 70’s and early 80’s scientists noticed that non-lysosomal intracellular proteolysis is dependent on ubiquitin and ATP [6]. ATP dependence was known since 1953, but dependence on ubiquitin was something new then. Ubiquitin participation in non-lysosomal intracellular proteolysis is said to be the main role of this protein in eukaryotic cells [23]. |
