Reaction: N6-(3-methylbut-2-en-1-yl)-adenine37 in tRNA + a [3Fe-4S] iron-sulfur cluster + 2 S-adenosyl-L-methionine + reduced electron acceptor = N6-(3-methylbut-2-en-1-yl)-2-(methylsulfanyl)adenine37 in tRNA + S-adenosyl-L-homocysteine + a [3Fe-3S] iron-sulfur cluster + L-methionine + 5'-deoxyadenine + electron acceptor
For diagram of reaction click here
Glossary: N6-(3-methylbut-2-en-1-yl)-adenine37 in tRNA = N6-dimethylallyladenine37 in tRNA
Other name(s): MiaB; 2-methylthio-N-6-isopentenyl adenosine synthase; tRNA-i6A37 methylthiotransferase
Systematic name: tRNA N6-(3-methylbut-2-en-1-yl)-adenine37:[3Fe-4S] iron-sulfur cluster,S-adenosyl-L-methionine C2-(methylsulfanyl)transferase
Comments: The enzyme is a member of the AdoMet radical (radical SAM) family. It contains one [4Fe-4S] cluster (the main cluster) and one [3Fe-4S] cluster (the auxiliary cluster). The reaction is thought to take place in two steps. In the first step, one molecule of SAM is used to methylate a bridging μ-sulfido ion of the auxiliary cluster, forming a thio-methyl group. In the second step, a second SAM molecule is cleaved to a 5'-deoxyadenosyl 5'-radical, which abstracts the C2 hydrogen of the substrate, and the thio-methyl group is transferred from the auxiliary cluster to the radical-activated carbon in the tRNA substrate. The auxiliary cluster is left in an inactive [3Fe-3S] state and must be repaired or replaced before the enzyme could catalyse the next round.
Links to other databases: BRENDA, EXPASY, GENE, KEGG, MetaCyc, PDB, CAS registry number
References:
1. Pierrel, F., Bjork, G.R., Fontecave, M. and Atta, M. Enzymatic modification of tRNAs: MiaB is an iron-sulfur protein. J. Biol. Chem. 277 (2002) 13367-13370. [PMID: 11882645]
2. Pierrel, F., Hernandez, H.L., Johnson, M.K., Fontecave, M. and Atta, M. MiaB protein from Thermotoga maritima. Characterization of an extremely thermophilic tRNA-methylthiotransferase. J. Biol. Chem. 278 (2003) 29515-29524. [PMID: 12766153]
3. Hernandez, H.L., Pierrel, F., Elleingand, E., Garcia-Serres, R., Huynh, B.H., Johnson, M.K., Fontecave, M. and Atta, M. MiaB, a bifunctional radical-S-adenosylmethionine enzyme involved in the thiolation and methylation of tRNA, contains two essential [4Fe-4S] clusters. Biochemistry 46 (2007) 5140-5147. [PMID: 17407324]
4. Landgraf, B.J., Arcinas, A.J., Lee, K.H. and Booker, S.J. Identification of an intermediate methyl carrier in the radical S-adenosylmethionine methylthiotransferases RimO and MiaB. J. Am. Chem. Soc. 135 (2013) 15404-15416. [PMID: 23991893]
5. Zhang, B., Arcinas, A.J., Radle, M.I., Silakov, A., Booker, S.J. and Krebs, C. First step in catalysis of the radical S-adenosylmethionine methylthiotransferase MiaB yields an intermediate with a [3Fe-4S]0-like auxiliary cluster. J. Am. Chem. Soc. 142 (2020) 1911-1924. [PMID: 31899624]
6. Esakova, O.A., Grove, T.L., Yennawar, N.H., Arcinas, A.J., Wang, B., Krebs, C., Almo, S.C. and Booker, S.J. Structural basis for tRNA methylthiolation by the radical SAM enzyme MiaB. Nature 597 (2021) 566-570. [PMID: 34526715]