Dual RING E3 Architectures Regulate Multiubiquitination and Ubiquitin Chain Elongation by APC/C

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Protein ubiquitination is a critical post-translational modification regulated by E1, E2, and E3 enzymes.
• E2 and RING E3 ligases collaborate to ubiquitinate substrates, leading to multiubiquitination or polyubiquitin chain elongation.

Purpose of the Study:

• To elucidate the specialized catalytic architectures of the human E3 anaphase-promoting complex/cyclosome (APC/C) and its E2 partners, UBE2C and UBE2S.
• To define the mechanisms by which APC/C-E2 interactions dictate distinct forms of polyubiquitination.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine high-resolution structures.
• Biochemical assays to analyze enzyme activity and substrate interactions.

Main Results:

• The APC/C RING constrains UBE2C for processive multiubiquitination by positioning it near the substrate and a substrate-linked ubiquitin.
• During chain elongation, the APC/C RING facilitates Lys11-linked chain formation by positioning UBE2S through a cullin interaction to capture an evolving substrate-linked ubiquitin.

Conclusions:

• Specialized E3-E2-substrate-ubiquitin architectures govern distinct polyubiquitination pathways.
• These findings reveal novel mechanisms of APC/C regulation and polyubiquitination control.