Giardia lamblia RNA cap guanine-N2 methyltransferase (Tgs2) Journal Article
| Authors: | Hausmann, S.; Shuman, S. |
| Article Title: | Giardia lamblia RNA cap guanine-N2 methyltransferase (Tgs2) |
| Abstract: | Tgs1 is the enzyme responsible for converting 7-methyl-guanosine RNA caps to the 2,2,7-trimethylguanosine cap structures of small nuclear and small nucleolar RNAs. Whereas budding yeast Saccharomyces cerevisiae and fission yeast Schizosaccharomyces pombe encode a single Tgs1 protein, the primitive eukaryote Giardia lamblia encodes two paralogs, Tgs1 and Tgs2. Here we show that purified Tgs2 is a monomeric enzyme that catalyzes methyl transfer from AdoMet (K m of 6 μM) to m 7GDP (K m of 65 μM; k cat of 14 min -1) to form m 2,7GDP. Tgs2 also methylates m 7GTP (K m of 30 μM; k cat of 13 min -1) and m 7GpppA (K m of 7 μM; k cat of 14 min -1) but is unreactive with GDP, GTP, GpppA, ATP, CTP, or UTP. We find that the conserved residues Asp-68, Glu-91, and Trp-143 are essential for Tgs2 methyltransferase activity in vitro. The m 2,7GDP product formed by Tgs2 can be converted to m 2,2,7GDP by S. pombe Tgs1 in the presence of excess AdoMet. However, Giardia Tgs2 itself is apparently unable to add a second methyl group at guanine-N2. This result implies that 2,2,7-trimethylguanosine caps in Giardia are either synthesized by Tgs1 alone or by the sequential action of Tgs2 and Tgs1. The specificity of Tgs2 raises the prospect that some Giardia mRNAs might contain dimethylguanosine caps. © 2005 The American Society for Biochemistry and Molecular Biology, Inc. |
| Keywords: | unclassified drug; methylation; sequence analysis; nonhuman; protein function; animals; dose-response relationship, drug; enzyme activity; transfection; time factors; rna; methyltransferase; methyltransferases; amino acid sequence; molecular sequence data; sequence homology, amino acid; kinetics; messenger rna; guanine; guanosine derivative; protein purification; saccharomyces cerevisiae; guanosine; eukaryota; nucleotide sequence; recombinant proteins; substrate specificity; green fluorescent proteins; amino acid; yeast; saccharomycetales; catalysis; adenosine triphosphate; small nucleolar rna; enzyme specificity; glutamic acid; guanosine triphosphate; aspartic acid; centrifugation, density gradient; catalyst; dinucleotide; enzymes; synthesis (chemical); hydrogen-ion concentration; monomer; tryptophan; macromolecular substances; schizosaccharomyces pombe; fission yeast; guanosine diphosphate; dimethylguanosine; giardia; capped rna; giardia lamblia; giardia intestinalis; glycerol; s adenosylmethionine; methyl group; 2,2,7 trimethylguanosine; small nuclear rna; cytidine triphosphate; monomers; trna methyltransferases; paralogy; 7 methylguanosine; protein tgs1; nucleolar rnas; sacchromyces; guanine n2 methyltransferase; protein tgs2; uridine triphosphate |
| Journal Title: | Journal of Biological Chemistry |
| Volume: | 280 |
| Issue: | 37 |
| ISSN: | 0021-9258 |
| Publisher: | American Society for Biochemistry and Molecular Biology |
| Date Published: | 2005-09-16 |
| Start Page: | 32101 |
| End Page: | 32106 |
| Language: | English |
| DOI: | 10.1074/jbc.M506438200 |
| PUBMED: | 16046409 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | --- - "Cited By (since 1996): 16" - "Export Date: 24 October 2012" - "CODEN: JBCHA" - "Molecular Sequence Numbers: GENBANK: EAA46438;" - "Source: Scopus" |
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