Removal of misfolded proteins from the ER is a consecutive process characterized by the interaction between many proteins in both the ER and the cytoplasm (Needham and Brodsky, 2013). To enter the ERAD pathway, the protein must be exported from the ER into the cytosol in a process known as retrotranslocation, also called dislocation. This retrotranslocation process occurs through the same translocon where the utilized proteins initially enter the ER: the Sec61 complex. This retrotranslocation channel present in the ER membrane is made up of several multiprotein complexes (Zhang et al., 2015). Each complex functions around a ubiquitin ligase in the membrane, an enzyme needed to recognize the target protein. Ubiquitin ligases are constituents of the ubiquitin proteasome system (UPS), a system that plays a critical role in ERAD. It is responsible for finding and destroying any proteins that are damaged or defective or simply in excess of the requirement. The UPS uses a protein called ubiquitin to target these faulty proteins in a process called ubiquitination. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essayThe process of ubiquitination is carried out by three different enzymes: ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2) and ubiquitin ligase (E3) and uses ATP as an energy source/E1 forms a high-energy thioester bond between a cysteine ​​residue present in its active site and the C-terminus of ubiquitin. This activated ubiquitin is then transferred to E2. E3 binds to the misfolded protein and aligns it so that the protein can bind with the ubiquitin attached to E2. An isopeptide bond is formed between the C-terminal glycine of ubiquitin and the lysine residues on the target protein. Several cycles of ubiquitination occur, forming a polyubiquitin chain (Nandi et al.). This polyubiquitin chain on the misfolded protein signals its degradation through the 19S cap complexes of the multi-subunit 26S proteasome. The proteasome binds and removes the polyubiquitin chain, unfolding the protein into smaller peptides. The protein is then reused for the synthesis of new proteins and the ubiquitin is recycled. Although the 26S proteasome recognizes poly-ubiquitinated proteins, the high specificity and selectivity of the UPS resides in several E3 enzymes, which are capable of recognizing a wide range of substrates (Wang and Maldonado). Hundreds of E3s exist in humans and are distinguished from each other by the presence of different domains: a RING-like (RING) domain or a HECT domain. RING domains transfer ubiquitin protein from E2 directly to the target substrate while HECT E3 domains transfer ubiquitin from E2 to E3 and then from E3 to the substrate (Berndsen and Wolberger, 2014). Although numerous studies have been conducted on E3 enzymes, the mechanisms by which they function and further increase ubiquitin transfer have yet to be considered (Berndsen and Wolberger, 2014). Research into how E3 ligases are regulated through interaction with different E2 enzymes and substrates may provide further insight into E3 specificity and reveal more about E ligase binding3.