Ubikvitiinointi

Ubikvitiinointi is a post-translational modification process in eukaryotic cells where a small regulatory protein called ubiquitin is attached to a target protein. This process is crucial for regulating a multitude of cellular functions. The attachment of ubiquitin, a process known as ubiquitination or conjugation, is a multi-step enzymatic reaction involving three key enzymes: E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin ligase). The E3 ligase plays a critical role in determining substrate specificity, thereby directing ubiquitination to specific target proteins.

Ubiquitination can occur as monoubiquitination (attachment of a single ubiquitin molecule) or polyubiquitination (attachment of a chain of ubiquitin molecules). The type of ubiquitination and the linkage formed between ubiquitin molecules within a polyubiquitin chain can dictate the fate of the target protein. Monoubiquitination and certain polyubiquitin chain linkages are often involved in signaling pathways, protein trafficking, and DNA repair. Conversely, the attachment of K48-linked polyubiquitin chains typically targets proteins for degradation by the proteasome, a large protein complex responsible for breaking down damaged or unwanted proteins. This degradation pathway is essential for maintaining cellular homeostasis and eliminating misfolded or terminally differentiated proteins. Dysfunction in ubiquitination pathways has been implicated in various diseases, including cancer and neurodegenerative disorders.