Structure analysis of the conserved methyltransferase domain of human trimethylguanosine synthase TGS1.
Methyltransferases play an important role in the post-transcriptional maturation of most ribonucleic acids. The modification of spliceosomal UsnRNAs includes N2-dimethylation of the m(7)G cap catalyzed by trimethylguanosine synthase 1 (TGS1). This 5'-cap hypermethylation occurs during the biogenesis of UsnRNPs as it initiates the m(3)G cap-dependent nuclear import of UsnRNPs. The conserved methyltransferase domain of human TGS1 has been purified, crystallized and the crystal structure of this domain with bound substrate m(7)GpppA was solved by means of multiple-wavelength anomalous dispersion. Crystal structure analysis revealed that m(7)GpppA binds via its adenosine moiety to the structurally conserved adenosylmethionine-binding pocket, while the m(7) guanosine remains unbound. This unexpected binding only occurs in the absence of AdoMet and suggests an incomplete binding pocket for the m(7)G cap which is caused by the N-terminal truncation of the protein. These structural data are consistent with the finding that the crystallized fragment of human TGS1 is catalytically inactive, while a fragment that is 17 amino acids longer exhibits activity.
Monecke
Thomas
T
Department of Molecular Structural Biology, Institute of Microbiology and Genetics, Georg-August-University Göttingen, Göttingen, Germany.
Dickmanns
Achim
A
Strasser
Anja
A
Ficner
Ralf
R
D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D006801:Humans; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012314:RNA Cap Analogs / Q000378:metabolism*; D012315:RNA Caps / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012436:S-Adenosylmethionine / Q000378:metabolism
D010446:Peptide Fragments; D012314:RNA Cap Analogs; D012315:RNA Caps; C509442:m7GpppA; D012436:S-Adenosylmethionine; D008780:Methyltransferases; C456271:trimethylguanosine synthase