Human Pumilio proteins use fuzzy multivalent hydrophobic interactions to recruit the CCR4-NOT deadenylase complex to...

Area of Science:

• Molecular Biology
• Gene Regulation
• Protein-RNA Interactions

Background:

• Pumilio (PUM) proteins are crucial RNA-binding proteins regulating gene expression during development and differentiation.
• Human PUM1 and PUM2 utilize an intrinsically disordered N-terminal repression domain (RD3) to recruit the CCR4-NOT deadenylase complex for mRNA repression.

Purpose of the Study:

• To dissect the mechanism by which the PUM protein repression domain (RD3) interacts with the CCR4-NOT complex.
• To elucidate the structural and compositional requirements for RD3-mediated gene repression.

Main Methods:

• Cell-based reporter assays to assess repression activity.
• Protein interaction assays using recombinant proteins.
• Crosslinking mass spectrometry to map protein-protein contacts.

Main Results:

• Short peptides within RD3 are sufficient for repression and directly bind the CNOT1, CNOT2, and CNOT3 subunits of the CCR4-NOT complex.
• Crosslinking data indicates multivalent, mutually exclusive interactions between RD3 and the NOT module, characteristic of a "fuzzy" binding mode.
• The physicochemical composition, specifically the distribution of aliphatic and aromatic residues, is critical for RD3 function, while linear amino acid sequence is dispensable.

Conclusions:

• Intrinsically disordered regions (IDRs) like RD3 employ low-affinity, multivalent interactions governed by amino acid composition to bind effector complexes.
• This mechanism provides robust PUM-mediated gene repression and exemplifies how IDRs recruit the CCR4-NOT complex for gene expression regulation.