Structural basis of mRNA cap recognition by Dcp1–Dcp2

Removal of the 5′ cap on mRNA by the decapping enzyme Dcp2 is a critical step in 5′-to-3′ mRNA decay. Understanding the structural basis of Dcp2 activity has been a significant challenge because Dcp2 is dynamic, with weak affinity for cap substrate. Here we present a 2.6-Å-resolution crystal structure of a heterotrimer of fission yeast Dcp2, its essential activator Dcp1, and the human NMD cofactor PNRC2, in complex with a tight-binding cap analog. Cap binding is accompanied by a conformational change of Dcp2 to form a composite nucleotide binding site using conserved residues on the catalytic and regulatory domains. Kinetic analysis of PNRC2 reveals a conserved short linear motif enhances both substrate affinity and the catalytic step of decapping. These findings explain why Dcp2 requires a conformational change for efficient catalysis and reveals that coactivators can promote RNA binding and the catalytic step of decapping, possibly through different conformational states.