UBIQUITIN RESEARCH TOOLS
Ubiquitin (Ub), a small (76 amino acids) polypeptide, is highly conserved among all living eukaryotes. Ubiquitin is covalently attached to cellular proteins and can regulate the levels, activity and localization of these proteins. Several ubiquitin-like proteins have been identified including SUMO, NEDD8 and ISG15. All of these UBLs utilize a similar mechanism for conjugation to target proteins. Briefly, energy is required to activate ubiquitin at its carboxy terminus; activation is catalysed by E1, which binds the Ub C-terminus to a side chain cysteine of the enzyme. The second enzyme of the series, E2 (called the ubiquitin conjugating protein), receives Ub as a thioester (Ub-CO-S-E1 - Ub-CO-S-E2); E2 then transfers Ub to a target polypeptide, which is bound to the third enzyme in the sequence, called E3, or Ubiquitin ligase. Thus, the E3 primarily determines the specificity of ubiquitylation. Poly-Ub chains can be formed via linkage of another Ub moiety to lysine 48 of the previous Ub protein. Other lysines may also serve as linkage sites in chain formation including lysine 63. It is important to note that not every Ub attachment results in formation of a poly-Ub tag. Attachment of a single Ub moiety to its target protein can modulate activity or localization. Ubiquitin is cleaved from substrates by deubiquitylating enzymes (also called ubiquitin hydrolases or ubiquitin isopeptidases). Isopeptidases are a family of cysteine proteases that specifically cleave ubiquitin-derived substrates of the general structure ubiquitin-X, where X = any number of leaving groups ranging from small thiols and amines to ubiquitin and other proteins. Thus, isopeptidases act to reverse the modification of proteins by ubiquitin or ubiquitin-like proteins. Modulation of cellular processes can be controlled by regulating protein ubiquitylation via modulation of E3 ligase and isopeptidase activity.
LifeSensors has the largest collection of ubiquitin research tools commercially available for studying the enzymes involved in this complex pathway. Using these tools scientists will be able to characterize enzyme function, identify substrates, discover modulators of this pathway, and make scientific breakthroughs that will deepen our understanding of the ubiquitin pathway. |
Fig 1. Ubiquitin conjugation pathway. Protein modification by ubiquitin requires sequential action of three enzymes: Ubiquitin activated by a specific activating enzyme (E1) to form a Ub-E1-thiolester. Activated Ub is transferred to a carrier protein or 'conjugase' E2, and then transferred to a ligase (E3) and linked via isopeptide bond to a lysine residue on the substrate protein. After linkage of Ub to the substrate, a polyUb chain can be formed in some cases. Ubiquitylated proteins can be deubiquitylated by specific isopeptidases. 
