Structure and mechanism of mRNA cap (guanine-N7) methyltransferase.
A suite of crystal structures is reported for a cellular mRNA cap (guanine-N7) methyltransferase in complex with AdoMet, AdoHcy, and the cap guanylate. Superposition of ligand complexes suggests an in-line mechanism of methyl transfer, albeit without direct contacts between the enzyme and either the N7 atom of guanine (the attacking nucleophile), the methyl carbon of AdoMet, or the sulfur of AdoMet/AdoHcy (the leaving group). The structures indicate that catalysis of cap N7 methylation is accomplished by optimizing proximity and orientation of the substrates, assisted by a favorable electrostatic environment. The enzyme-ligand structures, together with new mutational data, fully account for the biochemical specificity of the cap guanine-N7 methylation reaction, an essential and defining step of eukaryotic mRNA synthesis.
Fabrega
Carme
C
Biochemistry Department, Structural Biology Program, Weill Medical College, Cornell University, New York, NY 10021, USA.
Hausmann
Stéphane
S
Shen
Vincent
V
Shuman
Stewart
S
Lima
Christopher D
CD
D000409:Alanine / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D009670:Encephalitozoon cuniculi / Q000235:genetics; D008024:Ligands; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017354:Point Mutation; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000235:genetics; D012314:RNA Cap Analogs / Q000378:metabolism; D012315:RNA Caps; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D008024:Ligands; D015800:Protozoan Proteins; D012314:RNA Cap Analogs; D012315:RNA Caps; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D008780:Methyltransferases; D000409:Alanine