Molecular basis of RNA guanine-7 methyltransferase (RNMT) activation by RAM

Dhaval Varshney, Alain-Pierre Petit, Juan A. Bueren-Calabuig, Chimed Jansen, Dan A. Fletcher, Mark Peggie, Simone Weidlich, Paul Scullion, Andrei V. Pisliakov, Victoria H. Cowling (Lead / Corresponding author)

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18 Citations (Scopus)
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Abstract

Maturation and translation of mRNA in eukaryotes requires the addition of the 7-methylguanosine cap. In vertebrates, the cap methyltransferase, RNA guanine-7 methyltransferase (RNMT), has an activating subunit, RNMT-Activating Miniprotein (RAM). Here we report the first crystal structure of the human RNMT in complex with the activation domain of RAM. A relatively unstructured and negatively charged RAM binds to a positively charged surface groove on RNMT, distal to the active site. This results in stabilisation of a RNMT lobe structure which co-evolved with RAM and is required for RAM binding. Structure-guided mutagenesis and molecular dynamics simulations reveal that RAM stabilises the structure and positioning of the RNMT lobe and the adjacent α-helix hinge, resulting in optimal positioning of helix A which contacts substrates in the active site. Using biophysical and biochemical approaches, we observe that RAM increases the recruitment of the methyl donor, AdoMet (S-adenosyl methionine), to RNMT. Thus we report the mechanism by which RAM allosterically activates RNMT, allowing it to function as a molecular rheostat for mRNA cap methylation.

Original languageEnglish
Pages (from-to)10423-10436
Number of pages14
JournalNucleic Acids Research
Volume44
Issue number21
Early online date15 Jul 2016
DOIs
Publication statusPublished - 1 Dec 2016

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