Structural basis for Pan3 binding to Pan2 and its function in mRNA recruitment and deadenylation

Area of Science:

• Molecular Biology
• RNA Metabolism
• Protein-RNA Interactions

Background:

• The Pan2-Pan3 complex is crucial for shortening mRNA 3' polyA tails, a process known as deadenylation, which regulates mRNA stability in eukaryotes.
• While Pan2 possesses the exonuclease activity, the precise function of Pan3 in this complex has remained mechanistically unclear.

Purpose of the Study:

• To elucidate the mechanistic role of Pan3 in the Pan2-Pan3 deadenylation complex.
• To investigate the RNA-binding capabilities and interaction interface of Pan3 with Pan2.

Main Methods:

• Biochemical assays to assess RNA binding.
• Structural biology techniques, including X-ray crystallography, to determine the complex structure.
• Stoichiometry analysis of Pan2-Pan3 interaction.

Main Results:

• Pan3 directly binds RNA via its pseudokinase/C-terminal domain and specifically to polyA RNA through an N-terminal zinc finger.
• Pan2 alone exhibits no RNA binding activity.
• Pan3 binds the Pan2 linker region with a 2:1 stoichiometry, forming a high-affinity interaction.
• The crystal structure reveals how Pan3's asymmetric dimer facilitates interaction with Pan2.

Conclusions:

• Pan3 acts as an RNA-binding subunit, supplying polyA RNA substrates to the Pan2 exonuclease.
• This interaction is essential for the efficient deadenylation activity of the intact Pan2-Pan3 complex.
• The findings clarify the mechanistic contribution of Pan3 in mRNA deadenylation.