complex(a(MESH:Ubiquitin), p(HGNC:UBA2))

Components

• a(MESH:Ubiquitin)
• p(HGNC:UBA2)

The thioesterified ubiquitin passes from the E1 active site to the next member of the cascade, the E2 or ubiquitin-conjugating enzyme PubMed:24457024

E1s are multidomain enzymes that must activate ubiquitin and efficiently transfer it to the E2 active site PubMed:24457024

On the other hand, RING finger-containing E3s catalyze, most probably, direct transfer of the activated ubiquitin moiety from E2 to the E3 bound substrate PubMed:14556719

Some E3s can also stabilize the conformation between ubiquitin and the E2, thereby accelerating further the rate of conjugation of ubiquitin to proteins PubMed:24457024

Indeed, three recent structural studies observed the E2~ubiquitin conformation in the presence of either RING domains or the structurally related U-box domain [19–21] PubMed:24457024

Indeed, three recent structural studies observed the E2~ubiquitin conformation in the presence of either RING domains or the structurally related U-box domain [19–21] PubMed:24457024

Second, there is conjugation of the ATP-activated Ub to an E2 protein (i.e., a Ub-conjugating enzyme). PubMed:22908190

In summary, mechanisms of E2 activation involve the binding of ubiquitin to surfaces on the E2 and/or E3, thereby allowing an optimal conformation of ubiquitin on the E2 surface PubMed:24457024