Changes in conformational equilibria regulate the activity of the Dcp2 decapping enzyme.

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• Enzyme crystal structures are crucial for understanding molecular mechanisms.
• Determining enzyme structures in solution, especially for dynamic complexes, remains challenging.
• The bilobed decapping enzyme Dcp2 terminates gene expression by removing the 5' cap from eukaryotic mRNA.

Purpose of the Study:

• To investigate the solution structures of the Dcp2 enzyme.
• To correlate Dcp2 structural states with its catalytic cycle and activity.
• To understand how mRNA, Dcp1, and Edc1 influence Dcp2's dynamic equilibria and activity.

Main Methods:

• Methyl transverse relaxation-optimized NMR spectroscopy to study Dcp2 in solution.
• Analysis of existing crystal structures.
• Biochemical assays to assess Dcp2 activity and substrate specificity.

Main Results:

• Only three of the six observed crystal Dcp2 states are present in solution: open, closed, and catalytically active.
• mRNA substrate and activator proteins (Dcp1, Edc1) modulate the dynamic equilibria between these states.
• The active state requires both activators and mRNA or m7GDP for stable formation.
• Dcp2's activating mechanisms shift substrate specificity towards eukaryotic mRNA.

Conclusions:

• Dcp2 exhibits distinct dynamic equilibria in solution, differing from its numerous crystal structures.
• Activator and substrate binding are critical for stabilizing the catalytically active Dcp2 conformation.
• Understanding Dcp2's solution dynamics provides insights into mRNA decapping regulation and gene expression termination.