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Crystal structure of mRNA cap guanine-N7 methyltransferase obtained by limited proteolysis
Structural highlights
FunctionMCES_HUMAN mRNA-capping methyltransferase that methylates the N7 position of the added guanosine to the 5'-cap structure of mRNAs. Binds RNA containing 5'-terminal GpppC.[1] [2] [3] [4] Publication Abstract from PubMedMaturation 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 alpha-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. Molecular basis of RNA guanine-7 methyltransferase (RNMT) activation by RAM.,Varshney D, Petit AP, Bueren-Calabuig JA, Jansen C, Fletcher DA, Peggie M, Weidlich S, Scullion P, Pisliakov AV, Cowling VH Nucleic Acids Res. 2016 Jul 15. pii: gkw637. PMID:27422871[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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