MiaB protein is a bifunctional radical-S-adenosylmethionine enzyme involved in thiolation and methylation of tRNA

J Biol Chem. 2004 Nov 12;279(46):47555-63. doi: 10.1074/jbc.M408562200. Epub 2004 Aug 30.

Abstract

The last biosynthetic step for 2-methylthio-N(6)-isopentenyl-adenosine (ms(2)i(6)A), present at position 37 in some tRNAs, consists of the methylthiolation of the isopentenyl-adenosine (i(6)A) precursor. In this work we have reconstituted in vitro the conversion of i(6)A to ms(2)i(6)A within a tRNA substrate using the iron-sulfur MiaB protein, S-adenosylmethionine (AdoMet), and a reducing agent. We show that a synthetic i(6)A-containing RNA corresponding to the anticodon stem loop of tRNA(Phe) is also a substrate. This study demonstrates that MiaB protein is a bifunctional system, involved in both thiolation and methylation of i(6)A. In this process, one molecule of AdoMet is converted to 5'-deoxyadenosine, probably through reductive cleavage and intermediate formation ofa5'-deoxyadenosyl radical as observed in other "Radical-AdoMet" enzymes, and a second molecule of AdoMet is used as a methyl donor as shown by labeling experiments. The origin of the sulfur atom is discussed.

MeSH terms

  • Adenosine / chemistry
  • Adenosine / metabolism*
  • Animals
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins
  • Molecular Structure
  • Nucleic Acid Conformation
  • RNA, Transfer* / chemistry
  • RNA, Transfer* / genetics
  • RNA, Transfer* / metabolism
  • S-Adenosylmethionine / metabolism*
  • Sulfurtransferases / genetics
  • Sulfurtransferases / metabolism*
  • Thermotoga maritima / metabolism

Substances

  • Escherichia coli Proteins
  • S-Adenosylmethionine
  • RNA, Transfer
  • MiaB protein, E coli
  • Sulfurtransferases
  • isopentenyl-adenosine i6a thiotransferase
  • Adenosine