Ubiquitin chains: Difference between revisions

Ubiquitin chains (or polyubiquitin chains) are protein post-translational modifications that regulate proteasome dependent protein degradation, the cellular response to DNA damage, the inflammatory response and other cellular functions <ref>PMID: 19217402</ref><ref>PMID: 9367341</ref>. Chains begin as a single ubiquitin attached to the modified protein via an isopeptide linkage between a lysine side chain within the substrate protein and the C-terminal glycine of ubiquitin. The chain is built and extended by ubiquitination of ubiquitin on one of the lysines of ubiquitin or the N-terminus. There are a total of seven lysines in ubiquitin (K6, K11, K27, K29, K33, K48, and K63) and chains using all seven lysines have been identified <ref name=Xu>PMID: 19345192</ref>.  Chains are frequently referred to in the literature by the lysine position in ubiquitin that connects one ubiquitin to the next.  For example, chains built on lysine 48 of ubiquitin are called K48-linked chains. N-terminal to C-terminal connection of ubiquitin molecules is called a linear ubiquitin chain and chains which contain linkages through several lysine positions are called mixed chains <ref>PMID: 18516089</ref>. Ubiquitin chains with different linkages can have different cellular functions some of which are summarized below. The basis for the functional differences between polyubiquitin chains of different linkages were not apparent until the X-ray and NMR structures of several chains were solved.