Ub4ix – Other Categories

The ability to modify ubiquitin chains would be a useful research tool for understanding ubiquitin signalling in health and disease. The initial step in ubiquitin signalling is attachment of a ubiquitin molecule to a lysine residue, further ubiquitins can then be added to the initial monomer creating a chain. The chain length and location can affect the fate of the protein. The most well studied are lysine 48 (K48) linked ubiquitin chains. K48 polyubiquitin chains are recognised by deubiquitinating enzymes (DUBS) and targeted for proteasomal degradation. Macrocyclic peptides are being explored as ubiquitin ligands to better understand ubiquitin signalling. Ub4ix is a macrocyclic peptide that selectively binds to lysine48-linked ubiquitin dimer (K48-Ub2), with much higher affinity than linear counterparts. Importantly, binding of ub4ix to K48-Ub2 prevents recognition by DUBS thus inhibiting protein targeting for proteosomal degradation. This has been shown to promote apoptosis in cancer cells. Therefore, molecules like ub4ix could be a valuable tool in understanding ubiquitin signalling as well as lead to future disease treatments. Potentially, the ubiquitin system in could be a target for cancer therapy to alter the polyubiquitin recognition by interacting proteins, further work with ubi4x could provide vital steps along this path.