Fabien Pierrel
Study of the MiaB protein, a «Radical SAM» enzyme involved in tRNA modification
Published on 20 September 2004
Body text 1
Thesis presented September 20, 2004
Abstract:
Transfer RNAs (tRNAs) are key molecules of the translation mechanism because they perform the exact decoding of the messenger RNA (mRNA) inside the ribosome, allowing the synthesis of the protein corresponding to the mRNA. Mature tRNAs consist of 73 to 95 nucleotides among which modified nucleosides are found (86 different modified nucleosides identified to date). We studied one of these modified nucleosides: the 2-methylthio-N6-isopentenyladenosine (ms2i6A) which is present at position 37 of some tRNAs. The biosynthesis of ms2i6A is divided in 2 steps: first, a well characterized reaction of isopentenylation of the N6 position of adenosine 37 catalyzed by the MiaA protein and second, a methylthiolation of the 2 position of isopentenyladenosine 37 (i6A-37). At the beginning of our work, we knew only that this second step requires S-Adenosylmethionine (SAM), iron, L-cysteine and that at least one protein was involved in the reaction: the MiaB protein. With different
in vivo and
in vitro studies, we have shown that MiaB is a Fe-S containing protein which belongs to the recently identified « SAM Radical » superfamily. Members of this family use a particular radical activation mechanism. We have also shown that MiaB catalyzes both thiolation and methylation reactions of position 2 of i6A-37. The reaction of formation of the C-S bond onto the aromatic non reactive carbon atom 2 of i6A 37 is not yet understood but we bring some elements to answer the different questions which remain.
Keywords:
tRNA, modified nucleoside, ms2i6A, MiaB, SAM Radical, C-S bond
Download this thesis (Intranet link).
Top page