University of Zagreb. Faculty of Science. Department of Chemistry.
Abstract
Vjernost biosinteze proteina očuvana je točnim aminoaciliranjem specifične transfer-RNA (tRNA) pripadnom aminokiselinom i dekodiranjem pojedine aminoacilirane tRNA na ribosomu. Aminoacil-tRNA-sintetaze kataliziraju prvu reakciju te često stupaju u interakcije s drugim staničnim proteinima. U arheji Methanothermobacter thermautotrophicus arginil- i seril-tRNA-sintetaza (MtArgRS i MtSerRS) stupaju u prolaznu interakciju oblikujući kompleks. Metodom afinitetnog supročišćavanja i rezonancije površinskih plazmona s krnjim oblicima MtArgRS pokazano je da MtSerRS prepoznaje N-terminalni dio ArgRS, s naglaskom na elemente zadužene za prepoznavanje pripadne tRNA. Krnji oblici delta89-ArgRS i deltaNtot-ArgRS zamjetno oslabljeno vežu i aminoaciliraju pripadnu tRNA. S obzirom na prisutnost reakcijskih prekursora pokazano je da serilacijski intermedijeri ne utječu na stabilnost kompleksa ArgRS:SerRS. Dapače, molekula tRNASer može participirati u formiranju ternarnog kompleksa [SerRS:tRNASer]:ArgRS čija je stabilnost usporediva s onom binarnog kompleksa SerRS:ArgRS. Nasuprot tome, interakcija ovih proteina osjetljiva je na dodatak potpuno modificirane tRNAArg, koja dovodi do disocijacije proteinskog kompleksa. Transkripcija MttRNAArg u bakteriji E. coli rezultira nastankom triju karakterističnih molekulskih vrsta koje se razlikuju s obzirom na stupanj nadodanih posttranskripcijskih modifikacija. Istraživana arginil-tRNA-sintetaza aminoacilira takve supstrate s podjednakom učinkovitošću. Zanimljivo, SerRS inhibira arginilaciju lošijih supstrata, tj. manje modificiranih molekula tRNAArg. Uklanjanje djelomično modificiranih tRNA iz procesa translacije pokazuje kako ovaj proteinski kompleks djeluje poput osigurača čija je funkcija poboljšanje točnosti dekodiranja.The fidelity of protein biosynthesis is preserved by accurate aminoacylation of a specific transfer RNA (tRNA) with a cognate amino acid and the ribosomal decoding of each aminoacylated tRNA. Aminoacyl-tRNA synthetases (aaRS) catalyze the first reaction and are well known to interact with other cellular proteins. In the archaeon Methanothermo-bacter thermautotrophicus a complex is formed by the transient gathering of the arginyl- and seryl-tRNA synthetase (ArgRS and SerRS). Pull down and surface plasmon resonance experiments with truncated ArgRS variants showed that N-terminal part of ArgRS serves as the recognition platform for SerRS, with emphasis to the elements involved in tRNAArg recognition. Shortened variants delta89-ArgRS and deltaNtot-ArgRS show decreased ability for cognate tRNA binding and charging. Regarding the effect that reaction precursors may have on the stability of ArgRS:SerRS complex it is shown that serylation reaction precursors exert no influence. Furthermore, tRNASer is able to participate in ternary [SerRS:tRNASer]:ArgRS complex formation with the stability comparable to that of the binary SerRS:ArgRS assembly. In contrast, interaction of these proteins is susceptible to the addition of fully modified tRNAArg transcript which ultimately leads to dissociation of the complex. Overexpression of MttRNAArg in E. coli cells results with the production of three distinct molecular species which differ in the amount of added posttranscriptional modifications. Arginyl-tRNA synthetase investigated in this work aminoacylates such substrates with comparable efficacy. Interestingly, SerRS is able to inhibit arginylation of poorer substrates, i. e. less modified tRNAArg molecules. Elimination of the partly modified tRNAs from the translation process shows how this protein complex acts as a safeguarding switch improving decoding accuracy
