MiaB, a bifunctional radical-S-adenosylmethionine enzyme involved in the thiolation and methylation of tRNA, contains two essential [4Fe-4S] clusters

Biochemistry. 2007 May 1;46(17):5140-7. doi: 10.1021/bi7000449. Epub 2007 Apr 4.


The radical-S-adenosylmethionine (radical-AdoMet) enzyme MiaB catalyzes the posttranscriptional methylthiolation of N-6-isopentenyladenosine in tRNAs. Spectroscopic and analytical studies of the reconstituted wild-type and C150/154/157A triple variant forms of Thermotoga maritima MiaB have revealed the presence of two distinct [4Fe-4S](2+,1+) clusters in the protein. One is coordinated by the three conserved cysteines in the radical-AdoMet motif (Cys150, Cys154, and Cys157) as previously reported, and the other, here observed for the first time, is proposed to be coordinated by the three N-terminal conserved cysteines (Cys10, Cys46, and Cys79). The two [4Fe-4S]2+ clusters have similar UV-visible absorption, resonance Raman, and Mössbauer properties but differ in terms of redox properties and the EPR properties of the reduced [4Fe-4S]1+ clusters. Reconstituted forms of MiaB containing two [4Fe-4S] clusters are more active than previously reported. Comparison of MiaB with other radical-AdoMet enzymes involved in thiolation reactions, such as biotin synthase and lipoate synthase, is discussed as well as a possible role of the second cluster as a sacrificial S-donor in the MiaB-catalyzed reaction.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatography, High Pressure Liquid
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Iron-Sulfur Proteins / metabolism*
  • Methylation
  • RNA, Transfer / metabolism*
  • Spectrum Analysis / methods
  • Sulfhydryl Compounds / metabolism*
  • Sulfurtransferases / chemistry
  • Sulfurtransferases / metabolism*


  • Escherichia coli Proteins
  • Iron-Sulfur Proteins
  • Sulfhydryl Compounds
  • RNA, Transfer
  • MiaB protein, E coli
  • Sulfurtransferases