Structural basis of mRNA-cap recognition by Dcp1-Dcp2

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The decapping enzyme Dcp2 initiates 5'-to-3' mRNA decay by removing the 5' cap.
• Dcp2's dynamic nature and weak substrate affinity pose challenges to understanding its structure-activity relationship.
• Activators and cofactors are known to be essential for Dcp2 function.

Purpose of the Study:

• To elucidate the structural basis of Dcp2 decapping activity.
• To investigate the role of the activator Dcp1 and cofactor PNRC2 in Dcp2 function.
• To understand how substrate binding and coactivator interaction influence Dcp2 conformation and catalysis.

Main Methods:

• X-ray crystallography at 2.6-Å resolution to determine the structure of the Dcp2-Dcp1-PNRC2 complex.
• Biochemical assays, including kinetic analysis of PNRC2, to assess its impact on decapping.
• Site-directed mutagenesis and structural analysis to identify key residues involved in cap binding and catalysis.

Main Results:

• A high-resolution crystal structure of the fission yeast Dcp2-Dcp1-PNRC2 heterotrimer bound to a cap analog was obtained.
• Cap binding induces a conformational change in Dcp2, creating a composite nucleotide-binding site from conserved catalytic and regulatory residues.
• Kinetic analysis revealed that a conserved motif in PNRC2 significantly enhances both substrate affinity and the catalytic efficiency of decapping.

Conclusions:

• Dcp2 requires a conformational change for efficient decapping, facilitated by its interaction with activators and cofactors.
• Coactivators like PNRC2 play a crucial role in promoting both RNA binding and the catalytic step of decapping.
• The findings provide structural and mechanistic insights into mRNA decapping regulation and highlight the importance of coactivator-induced conformational dynamics.