Ubiquitin is a small regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ubiquitously. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Four genes in the human genome code for ubiquitin: UBB, UBC, UBA52 and RPS27A.
Von Hippel–Lindau disease (VHL), also known as VonHippel–Lindau syndrome, is a rare genetic disorder with multisystem involvement. It is characterized by visceral cysts and benign tumors with potential for subsequent malignant transformation. It is a type of phakomatosis that results from a mutation in the Von Hippel–Lindau tumor suppressor gene on chromosome 3p25.3.
A ubiquitin ligase is a protein that recruits an E2 ubiquitin-conjugating enzyme that has been loaded with ubiquitin, recognizes a protein substrate, and assists or directly catalyzes the transfer of ubiquitin from the E2 to the protein substrate. In simple and more general terms, the ligase enables movement of ubiquitin from a ubiquitin carrier to another thing by some mechanism. The ubiquitin, once it reaches its destination, ends up being attached by an isopeptide bond to a lysine residue, which is part of the target protein. E3 ligases interact with both the target protein and the E2 enzyme, and so impart substrate specificity to the E2. Commonly, E3s polyubiquitinate their substrate with Lys48-linked chains of ubiquitin, targeting the substrate for destruction by the proteasome. However, many other types of linkages are possible and alter a protein's activity, interactions, or localization. Ubiquitination by E3 ligases regulates diverse areas such as cell trafficking, DNA repair, and signaling and is of profound importance in cell biology. E3 ligases are also key players in cell cycle control, mediating the degradation of cyclins, as well as cyclin dependent kinase inhibitor proteins. The human genome encodes over 600 putative E3 ligases, allowing for tremendous diversity in substrates.
Deubiquitinating enzymes (DUBs), also known as deubiquitinating peptidases, deubiquitinating isopeptidases, deubiquitinases, ubiquitin proteases, ubiquitin hydrolases, ubiquitin isopeptidases, are a large group of proteases that cleave ubiquitin from proteins. Ubiquitin is attached to proteins in order to regulate the degradation of proteins via the proteasome and lysosome; coordinate the cellular localisation of proteins; activate and inactivate proteins; and modulate protein-protein interactions. DUBs can reverse these effects by cleaving the peptide or isopeptide bond between ubiquitin and its substrate protein. In humans there are nearly 100 DUB genes, which can be classified into two main classes: cysteine proteases and metalloproteases. The cysteine proteases comprise ubiquitin-specific proteases (USPs), ubiquitin C-terminal hydrolases (UCHs), Machado-Josephin domain proteases (MJDs) and ovarian tumour proteases (OTU). The metalloprotease group contains only the Jab1/Mov34/Mpr1 Pad1 N-terminal+ (MPN+) (JAMM) domain proteases.
Hemangioblastomas, or haemangioblastomas, are vascular tumors of the central nervous system that originate from the vascular system, usually during middle age. Sometimes, these tumors occur in other sites such as the spinal cord and retina. They may be associated with other diseases such as polycythemia, pancreatic cysts and Von Hippel–Lindau syndrome. Hemangioblastomas are most commonly composed of stromal cells in small blood vessels and usually occur in the cerebellum, brainstem or spinal cord. They are classed as grade I tumors under the World Health Organization's classification system.
The Von Hippel–Lindau tumor suppressor also known as pVHL is a protein that, in humans, is encoded by the VHL gene. Mutations of the VHL gene are associated with Von Hippel–Lindau disease.
Hypoxia-inducible factor 1-alpha, also known as HIF-1-alpha, is a subunit of a heterodimeric transcription factor hypoxia-inducible factor 1 (HIF-1) that is encoded by the HIF1A gene. The Nobel Prize in Physiology or Medicine 2019 was awarded for the discovery of HIF.
Elongin C is a protein that in humans is encoded by the ELOC gene.
Elongin B is a protein that in humans is encoded by the ELOB gene.
USP26 is a peptidase enzyme. The USP26 gene is an X-linked gene exclusively expressed in the testis and it codes for the ubiquitin-specific protease 26. The USP26 gene is found at Xq26.2 on the X-chromosome as a single exon. The enzyme that this gene encodes comprises 913 amino acid residues and it is 104 kilodalton in size, which is transcribed from a sequence of 2794 nucleotide base-pairs on the X-chromosome. The USP26 enzyme is a deubiquitinating enzyme that places a very significant role in the regulation of protein turnover during spermatogenesis. It is a testis-specific enzyme that is solely express in spermatogonia and can prevent the degradation of ubiquitinated USP26 substrates.
Ubiquitin carboxyl-terminal hydrolase 16 is an enzyme that in humans is encoded by the USP16 gene.
Ubiquitin specific protease 4 (USP4) is an enzyme that cleaves ubiquitin from a number of protein substrates. Prior to the standardization of nomenclature USP4 was known as UNP, and was one of the first deubiquitinating enzymes to be identified in mammals. In the mouse and human the USP4 protein is encoded by a gene containing 22 exons.
Ubiquitin carboxyl-terminal hydrolase or Ubiquitin specific protease 11 is an enzyme that in humans is encoded by the USP11 gene. USP11 belongs to the Ubiquitin specific proteases family (USPs) which is a sub-family of the Deubiquitinating enzymes (DUBs).USPs are multiple domain proteases and belong to the C19 cysteine proteases sub‒family. Depending on their domain architecture and position there is different homology between the various members. Generally the largest domain is the catalytic domain which harbours the three residue catalytic triad that is included inside conserved motifs. The catalytic domain also contains sequences that are not related with the catalysis function and their role is mostly not clearly understood at present, the length of these sequences varies for each USP and therefore the length of the whole catalytic domain can range from approximately 295 to 850 amino acids. Particular sequences inside the catalytic domain or at the N‒terminus of some USPs have been characterised as UBL and DUSP domains respectively. In some cases, regarding the UBL domains, it has been reported to have a catalysis enhancing function as in the case of USP7. In addition, a so‒called DU domain module is the combination of a DUSP domain followed by a UBL domain separated by a linker and is found in USP11 as well as in USP15 and USP4.
Ubiquitin specific peptidase 18 (USP18), also known as UBP43, is a type I interferon receptor repressor and an isopeptidase. In humans, it is encoded by the USP18 gene. USP18 is induced by the immune response to type I and III interferons, and serves as a negative regulator of type I interferon, but not type III interferon. Loss of USP18 results in increased responsiveness to type I interferons and life-threatening autoinflammatory disease in humans due to the negative regulatory function of USP18 in interferon signal transduction. Independent of this activity, USP18 is also a member of the deubiquitinating protease family of enzymes. It is known to remove ISG15 conjugates from a broad range of protein substrates, a process known as deISGylation.
Ubiquitin-specific protease 36 is an enzyme that in humans is encoded by the USP36 gene.
Ubiquitin carboxyl-terminal hydrolase 33 is an enzyme that in humans is encoded by the USP33 gene.
Ubiquitin carboxyl-terminal hydrolase 48 is an enzyme that in humans is encoded by the USP48 gene.
Ubiquitin carboxyl-terminal hydrolase 2 is an enzyme that in humans is encoded by the USP2 gene.
Ubiquitin-specific protease 14 is an enzyme that in humans is encoded by the USP14 gene.
The ubiquitin carboxyl-terminal hydrolase 27, also known as deubiquitinating enzyme 27, ubiquitin thioesterase 27 and USP27X, is a deubiquitinating enzyme which is mainly characterized for cleaving ubiquitin (Ub) from proteins and other molecules. Ubiquitin binds to proteins so as to regulate the degradation of them via the proteasome and lysosome among many other functions.
