title: West Nile virus methyltransferase catalyzes two methylations of the viral RNA cap through a substrate-repositioning mechanism.
abstract: Flaviviruses encode a single methyltransferase domain that sequentially catalyzes two methylations of the viral RNA cap, GpppA-RNA-->m(7)GpppA-RNA-->m(7)GpppAm-RNA, by using S-adenosyl-l-methionine (SAM) as a methyl donor. Crystal structures of flavivirus methyltransferases exhibit distinct binding sites for SAM, GTP, and RNA molecules. Biochemical analysis of West Nile virus methyltransferase shows that the single SAM-binding site donates methyl groups to both N7 and 2'-O positions of the viral RNA cap, the GTP-binding pocket functions only during the 2'-O methylation, and two distinct sets of amino acids in the RNA-binding site are required for the N7 and 2'-O methylations. These results demonstrate that flavivirus methyltransferase catalyzes two cap methylations through a substrate-repositioning mechanism. In this mechanism, guanine N7 of substrate GpppA-RNA is first positioned to SAM to generate m(7)GpppA-RNA, after which the m(7)G moiety is repositioned to the GTP-binding pocket to register the 2'-OH of the adenosine with SAM, generating m(7)GpppAm-RNA. Because N7 cap methylation is essential for viral replication, inhibitors designed to block the pocket identified for the N7 cap methylation could be developed for flavivirus therapy.
authors.affiliation: Wadsworth Center, New York State Department of Health, Albany, New York 12201, USA. ship@wadsworth.org
authors.forename: Hongping
authors.initials: H
authors.lastname: Dong
authors.forename: Suping
authors.initials: S
authors.lastname: Ren
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Yangsheng
authors.initials: Y
authors.lastname: Zhou
authors.forename: Francesc
authors.initials: F
authors.lastname: Puig-Basagoiti
authors.forename: Hongmin
authors.initials: H
authors.lastname: Li
authors.forename: Pei-Yong
authors.initials: PY
authors.lastname: Shi
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D006160:Guanosine Triphosphate / Q000378:metabolism; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism*; D012315:RNA Caps / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism; D014902:West Nile virus / Q000201:enzymology*
chemical_list: D012315:RNA Caps; D012436:S-Adenosylmethionine; D006160:Guanosine Triphosphate; D008780:Methyltransferases