7-methylguanosine diphosphate (m7GDP) is not hydrolyzed but strongly bound by Decapping Scavenger (DcpS) enzymes and potently inhibits their activity

摘要

Decapping scavenger (DcpS) enzymes catalyze the cleavage of a residual cap structure following 3′→5′ mRNA decay. Some previous studies suggested that both m⁷GpppG and m⁷GDP were substrates for DcpS hydrolysis. Herein, we show that mononucleoside diphosphates, m⁷GDP (7-methylguanosine diphosphate) and m3^2,2,7GDP (2,2,7-trimethylguanosine diphosphate), resulting from mRNA decapping by the Dcp1/2 complex in the 5′→3′ mRNA decay, are not degraded by recombinant DcpS proteins (human, nematode and yeast). Furthermore, whereas mononucleoside diphosphates (m⁷GDP and m3^2,2,7GDP) are not hydrolyzed by DcpS, mononucleoside triphosphates (m⁷GTP and m3^2,2,7GTP) are, demonstrating the importance of a triphosphate chain for DcpS hydrolytic activity. m⁷GTP and m3^2,2,7GTP are cleaved at a slower rate than their corresponding dinucleotides (m⁷GpppG and m3^2,2,7GpppG, respectively), indicating an involvement of the second nucleoside for efficient DcpS-mediated digestion. Although DcpS enzymes cannot hydrolyze m⁷GDP, they have a high binding affinity for m⁷GDP and m⁷GDP potently inhibits DcpS hydrolysis of m⁷GpppG, suggesting that m⁷GDP may function as an efficient DcpS inhibitor. Our data have important implications for the regulatory role of m⁷GDP in mRNA metabolic pathways, due to its possible interactions with different cap-binding proteins, such as DcpS or eIF4E.