Ubiquitiniinivälitys

Ubiquitiniinivälitys, often translated as ubiquitination or ubiquitinylation, is a critical post-translational modification in eukaryotic cells. It involves the covalent attachment of a small protein called ubiquitin to a target protein. This process is mediated by a cascade of three enzymes: E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin ligase). The E1 enzyme activates ubiquitin, which is then transferred to an E2 enzyme. Finally, the E3 ligase provides specificity, recognizing the target protein and facilitating the transfer of ubiquitin from the E2 to the substrate.

Ubiquitiniinivälitys can occur as a single ubiquitin molecule (monoubiquitination) or as chains of ubiquitin molecules (polyubiquitination). The type and linkage of the ubiquitin chain determine the fate of the target protein. Monoubiquitination and certain polyubiquitin chain linkages can regulate protein function, localization, and interactions. However, polyubiquitin chains linked through lysine 48 (K48) are a primary signal for proteasomal degradation, marking the protein for destruction. Other ubiquitin linkages, such as K63, are often involved in non-degradative roles, including DNA repair and signal transduction. The reversibility of ubiquitiniinivälitys is also important, as deubiquitinating enzymes (DUBs) can remove ubiquitin tags, thereby reversing the modification and its consequences. This dynamic process is fundamental to numerous cellular processes and disruptions in ubiquitiniinivälitys are implicated in various diseases.