Abstract
Through the combined action of ubiquitinating and deubiquitinating enzymes, conjugation of ubiquitin to a target protein acts as a reversible post-translational modification functionally similar to phosphorylation. Indeed, ubiquitination is more and more recognized as a central process for the fine regulation of many cellular pathways. Due to their nature as obligate intracellular parasites, viruses rely on the most conserved host cell machineries for their own replication. Thus, it is not surprising that members from almost every viral family are challenged by ubiquitin mediated mechanisms in different steps of their life cycle and have evolved in order to by-pass or exploit the cellular ubiquitin conjugating system to maximize their chance to establish a successful infection. In this review we will present several examples of the complex interplay that links viruses and the ubiquitin conjugation machinery, with a special focus on the mechanisms evolved by the human immunodeficiency virus to escape from cellular restriction factors and to exit from infected cells.
Highlights
Ubiquitin (Ub) is a highly conserved protein of 76 aminoacids that can be covalently linked to target proteins through a multistep process known as ubiquitination
Protein ubiquitination involves a series of cellular enzymes in an enzymatic cascade, starting with the Ub-activating enzyme E1, followed by the ubiquitin-conjugating enzyme E2 and by the Ub ligase E3, which form an isopeptide bond between the carboxyl terminus of Ub and the ε-amino group of a lysine residue on the target protein [2]
cullin-RING finger Ub ligases (CRLs) are the largest family of Ub ligases and are responsible for ubiquitination of almost 20% of cellular proteins degraded through the Ub-proteasome system (UPS)
Summary
Ubiquitin (Ub) is a highly conserved protein of 76 aminoacids that can be covalently linked to target proteins through a multistep process known as ubiquitination. It has become clear that members of almost all viral families subvert or exploit both the cellular Ub-conjugating and -deconjugating machineries in different phases of their replication cycle [15,16,17,18,19,20,21,22,23,24,25,26,27,28] Under this respect, studies based on the treatment of infected cells with proteasome inhibitors have been instrumental, as such a treatment blocks the UPS, and depletes the cellular pool of free Ub, affecting de facto all the cellular pathways involving this protein. Ub plays a role in viral release from infected cells [40], as it will be discussed in more details later on
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