Monoubiquitinazione

Monoubiquitinazione is a type of post-translational modification where a single ubiquitin molecule is covalently attached to a substrate protein. Ubiquitin is a small, highly conserved protein that plays a crucial role in various cellular processes. The attachment of ubiquitin is typically mediated by a cascade of enzymes: an E1 ubiquitin-activating enzyme, an E2 ubiquitin-conjugating enzyme, and an E3 ubiquitin ligase. The E3 ligase provides specificity, recognizing the target protein and facilitating the transfer of ubiquitin from the E2 enzyme to a lysine residue on the substrate.

Unlike polyubiquitination, which involves the formation of ubiquitin chains, monoubiquitination results in the addition of just one ubiquitin molecule. This modification can occur on lysine residues, but also on other amino acids like cysteine, serine, or threonine, depending on the specific E3 ligase and context.

Monoubiquitination serves as a signal for a wide array of cellular functions. It can alter the protein's localization within the cell, influence its interaction with other proteins, or modulate its activity. Key processes regulated by monoubiquitination include protein trafficking, DNA repair, gene transcription, endocytosis, and signal transduction pathways. For example, monoubiquitination of certain receptor proteins can signal their internalization into the cell via endocytosis. It can also act as a regulatory switch, turning protein activity on or off. The reversible nature of monoubiquitination, with deubiquitinating enzymes (DUBs) capable of removing the ubiquitin tag, allows for dynamic control of these cellular processes.