Cap analog substrates reveal three clades of cap guanine-N2 methyltransferases with distinct methyl acceptor specificities Journal Article
| Authors: | Benarroch, D.; Jankowska-Anyszka, M.; Stepinski, J.; Darzynkiewicz, E.; Shuman, S. |
| Article Title: | Cap analog substrates reveal three clades of cap guanine-N2 methyltransferases with distinct methyl acceptor specificities |
| Abstract: | The Tgs proteins are structurally homologous AdoMet-dependent eukaryal enzymes that methylate the N2 atom of 7-methyl guanosine nucleotides. They have an imputed role in the synthesis of the 2,2,7-trimethylguanosine (TMG) RNA cap. Here we exploit a collection of cap-like substrates to probe the repertoire of three exemplary Tgs enzymes, from mammalian, protozoan, and viral sources, respectively. We find that human Tgs (hTgs1) is a bona fide TMG synthase adept at two separable transmethylation steps: (1) conversion of m7G to m2,7G, and (2) conversion of m2,7G to m2,2,7G. hTgs1 is unable to methylate G or m2G, signifying that both steps require an m7G cap. hTgs1 utilizes a broad range of m7G nucleotides, including mono-, di-, tri-, and tetraphosphate derivatives as well as cap dinucleotides with triphosphate or tetraphosphate bridges. In contrast, Giardia lamblia Tgs (GlaTgs2) exemplifies a different clade of guanine-N2 methyltransferase that synthesizes only a dimethylguanosine (DMG) cap structure and cannot per se convert DMG to TMG under any conditions tested. Methylation of benzyl7G and ethyl7G nucleotides by hTgs1 and GlaTgs2 underscored the importance of guanine N7 alkylation in providing a key π-cation interaction in the methyl acceptor site. Mimivirus Tgs (MimiTgs) shares with the Giardia homolog the ability to catalyze only a single round of methyl addition at guanine-N2, but is distinguished by its capacity for guanine-N2 methylation in the absence of prior N7 methylation. The relaxed cap specificity of MimiTgs is revealed at alkaline pH. Our findings highlight both stark and subtle differences in acceptor specificity and reaction outcomes among Tgs family members. Published by Cold Spring Harbor Laboratory Press. Copyright © 2010 RNA Society. |
| Keywords: | unclassified drug; methylation; nonhuman; metabolism; mammalia; classification; protein; ph; enzymology; enzyme activity; enzyme substrate; physiology; rna; methyltransferase; methyltransferases; enzyme analysis; guanosine; rna caps; eukaryota; mimivirus; substrate specificity; drug derivative; alkylation; catalysis; enzyme specificity; enzyme structure; catalytic domain; protozoa; hydrogen-ion concentration; enzyme active site; cap hypermethylation; dimethylguanosine; giardia; rna methyltransferase; tgs protein; capped rna; n(2),n(2),7 trimethylguanosine; n(2),n(2),7-trimethylguanosine; trimethylguanosine synthase; cladistics; giardia lamblia; human versus nonhuman data; rna capping; giardia intestinalis; mimiviridae; rna cap analogs |
| Journal Title: | RNA |
| Volume: | 16 |
| Issue: | 1 |
| ISSN: | 1355-8382 |
| Publisher: | Cold Spring Harbor Laboratory Press |
| Date Published: | 2010-01-01 |
| Start Page: | 211 |
| End Page: | 220 |
| Language: | English |
| DOI: | 10.1261/rna.1872110 |
| PUBMED: | 19926722 |
| PROVIDER: | scopus |
| PMCID: | PMC2802030 |
| DOI/URL: | |
| Notes: | --- - "Cited By (since 1996): 1" - "Export Date: 20 April 2011" - "CODEN: RNARF" - "Source: Scopus" |
Altmetric
Citation Impact
BMJ Impact Analytics
Related MSK Work