ubiquitin conjugating enzyme activity

Definition

Target type: molecularfunction

Isoenergetic transfer of ubiquitin from one protein to another via the reaction X-ubiquitin + Y = Y-ubiquitin + X, where both the X-ubiquitin and Y-ubiquitin linkages are thioester bonds between the C-terminal glycine of ubiquitin and a sulfhydryl side group of a cysteine residue. [GOC:BioGRID, GOC:dph]

Ubiquitin conjugating enzyme (E2) activity is a critical step in the ubiquitin-proteasome system (UPS), a major cellular pathway responsible for protein degradation. This activity is catalyzed by E2 enzymes, which act as molecular chaperones that facilitate the transfer of ubiquitin (Ub), a small, highly conserved protein, from an E1 ubiquitin-activating enzyme to a target protein.

The molecular function of E2 enzymes can be broken down into several key steps:

1. **Binding of ubiquitin:** E2 enzymes possess a conserved catalytic cysteine residue within their active site, which forms a covalent thioester bond with the C-terminal glycine residue of ubiquitin. This binding event is facilitated by the E1 enzyme, which initially activates ubiquitin through ATP hydrolysis.

2. **Transfer of ubiquitin:** Once ubiquitin is bound to the E2 enzyme, the complex can interact with an E3 ubiquitin ligase, a protein that recognizes specific target proteins. The E3 ligase brings the E2-ubiquitin complex into proximity with the target protein, allowing for the transfer of ubiquitin from the E2 to a lysine residue on the target protein.

3. **Formation of polyubiquitin chains:** The transfer of ubiquitin to the target protein can be repeated, leading to the formation of polyubiquitin chains. These chains are typically linked through the lysine residues of ubiquitin, and the specific type of chain formed (e.g., K48, K63) determines the fate of the target protein. K48-linked chains signal for proteasomal degradation, while K63-linked chains can be involved in a variety of cellular processes, such as DNA repair and signal transduction.

4. **Regulation of protein activity:** In addition to degradation, ubiquitination can also regulate protein activity by altering their interactions with other proteins or by affecting their localization within the cell.

Overall, E2 enzymes play a crucial role in the UPS by mediating the transfer of ubiquitin to target proteins. This process is essential for maintaining protein homeostasis, regulating protein activity, and eliminating misfolded or damaged proteins. The specific activity of E2 enzymes is determined by their interactions with different E1 enzymes, E3 ligases, and target proteins, contributing to the diverse regulatory functions of the UPS.'
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Proteins (1)

Compounds (3)