OTUB1 co-opts Lys48-linked ubiquitin recognition to suppress E2 enzyme function

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Biology

Background:

• Ubiquitylation is a crucial post-translational modification mediated by E1, E2, and E3 enzymes.
• OTUB1, a deubiquitylase, was previously shown to inhibit the DNA damage response independent of its enzymatic activity.
• OTUB1 inhibits ubiquitin transfer by E2 enzymes like UBC13, UBE2D, and UBE2E.

Purpose of the Study:

• To elucidate the structural mechanism by which OTUB1 binds E2 enzymes and inhibits ubiquitin transfer.
• To understand how OTUB1's interaction with E2s impacts the DNA damage response.

Main Methods:

• X-ray crystallography to determine the structure of OTUB1 bound to E2 enzymes and ubiquitin.
• Biochemical assays to measure ubiquitin transfer activity in the presence of OTUB1 and ubiquitin.

Main Results:

• OTUB1 recognizes ubiquitin-charged E2 enzymes through interactions with both the donor ubiquitin and the E2 enzyme.
• Free ubiquitin binds to OTUB1's distal ubiquitin-binding site, promoting the formation of an inhibited E2 complex.
• The binding configuration mimics Lys48-linked ubiquitin chain cleavage products, with Lys48 of donor ubiquitin positioned near OTUB1's catalytic site.

Conclusions:

• OTUB1 employs a novel mechanism to inhibit ubiquitin conjugation by hijacking Lys48-linked ubiquitin chain recognition.
• This interaction suppresses E2 enzyme activity, thereby inhibiting the DNA damage response.
• The findings provide structural insights into deubiquitylase regulation and its role in DNA repair pathways.