UPF1 helicase orchestrates mutually exclusive interactions with the SMG6 endonuclease and UPF2

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Nonsense-mediated mRNA decay (NMD) is a crucial pathway for degrading aberrant mRNAs and regulating gene expression.
• The UPF1 RNA helicase is central to NMD, interacting with various protein factors.
• SMG6 endonuclease recruitment to UPF1 is essential for mRNA cleavage in human NMD.

Purpose of the Study:

• To elucidate the molecular mechanism underlying the interaction between SMG6 and UPF1 in NMD.
• To identify and characterize the specific motif mediating the UPF1-SMG6 interaction.
• To understand how UPF2 binding to UPF1 influences SMG6 recruitment.

Main Methods:

• Mass spectrometry to identify interacting partners and motifs.
• Structural biology (cryo-EM) to determine complex structures.
• Biochemical assays to validate interactions and functional mechanisms.

Main Results:

• A conserved short linear motif in SMG6 was identified, interacting with the UPF1 cysteine/histidine-rich (CH) domain.
• UPF1-SMG6 interaction is inhibited when the UPF1 CH domain is bound by UPF2.
• Distinct SMG6- and UPF2-containing NMD complexes are proposed, regulated by UPF1's RNA-binding status and conformational states.

Conclusions:

• The findings provide a mechanistic explanation for SMG6 recruitment in metazoan NMD.
• The study advances the understanding of how UPF1's interactions regulate NMD complex formation and SMG6 endonuclease activity.
• This work clarifies mechanisms governing substrate recognition and activity within the NMD pathway.