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Review
. 2012 Nov;1824(11):1223-30.
doi: 10.1016/j.bbapap.2011.11.007. Epub 2011 Dec 7.

The methylthiolation reaction mediated by the Radical-SAM enzymes

Mohamed Atta  1 , Simon Arragain, Marc Fontecave, Etienne Mulliez, John F Hunt, Jon D Luff, Farhad Forouhar
Affiliations
Review

The methylthiolation reaction mediated by the Radical-SAM enzymes

Mohamed Atta et al. Biochim Biophys Acta. 2012 Nov.

Abstract

Over the past 10 years, considerable progress has been made in our understanding of the mechanistic enzymology of the Radical-SAM enzymes. It is now clear that these enzymes appear to be involved in a remarkably wide range of chemically challenging reactions. This review article highlights mechanistic and structural aspects of the methylthiotransferases (MTTases) sub-class of the Radical-SAM enzymes. The mechanism of methylthio insertion, now observed to be performed by three different enzymes is an exciting unsolved problem. This article is part of a Special Issue entitled: Radical SAM enzymes and Radical Enzymology.

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Figures

Figure 1
Figure 1. Phylogenetic analysis of MTTase families
Cladogram showing representatives from all MTTase famlies identified via comprehensive sequence analysis of 971 eubacterial and archaeabacterial genomes. Divisions between families were established based on simultaneous encoding of members of two families in a single genome. The total count of such occurrences is indicated in the table at the bottom left. MTTases were identified via an all-versus-all BLAST analysis of the full set of genomes, which yielded 813 sequences containing all three characteristic domains (UPF0004, Radical-SAM, and TRAM). Sequences occurring simultaneously in a single genome were used for an initial clustering, which was confirmed by back-tracing of the branches of the phylogenetic tree to ensure that splits between families are supported by such simultaneous occurrences. No more than one member of each family is encoded in a single genome (as indicated by the numbers on the diagonal in the table).
Figure 2
Figure 2. Structural organization of MTTases
The stereopair shows the inferred position of the UPF0004 domain (light green ellipse) relative to a ribbon diagram of the Radical-SAM (yellow) and TRAM (orange) domains from the crystal structure of a truncated apo construct of Thermotoga maritima RimO [15]. The approximate locations where the [4Fe-4S] cluster (cyan spheres) and SAM (stick representation) bind to the Radical-SAM domain were inferred by alignment of the homologous regions of the Radical-SAM domain from the crystal structure of holo MoaA [20]. The second [4Fe-4S] cluster present in enzymatically active RimO is likely to be bound by the invariant cys residues in the UPF004 domain. (See text.) Based on the location of the N-terminus of the Radical-SAM domain, which follows the UPF0004 domain in the primary sequence, the [4Fe-4S] cluster bound to the UPF0004 domain is likely to proximal to the Radical-SAM active site. Carbon is colored cyan, nitrogen blue, oxygen red, and sulfur yellow in the SAM molecule.
Figure 3
Figure 3. Radical-based mechanisms in post-transcriptional and posttranslational modifications
(A) methylthiolation of aromatic carbons C2, R = -CH2-CH=C(CH3)2 for ms2i6A biosynthesis or -CO-NH-CH(CH(CH3)OH-COOH for ms2t6A production. (B) 3-methythio aspartate formation. Ado˙; 5’-deoxyadenosyl radical, AdoH; 5’-deoxyadenosyl, SAM; S-adenosylmethionine, SAH; S-adenosylhomocystein.
Scheme 1
Scheme 1. The two strategies for production of highly oxidant species involved in the C-H bond activation
(A) Mechanisms proposed for O2 activation to yield high-valent-iron-oxo by haem iron enzymes (1) and non-haem iron enzymes (2). P, porphyrin. (B) Mechanism for the reductive cleavage of SAM by [4Fe-4S] cluster of Radical-SAM enzymes to yield 5’-deoxyadenosyl radical Ado˙. SAM is ligated through the amino and carboxylate groups to the unique iron (bleu) in the [4Fe-4S]+1 cluster. e−, electron; SAM, S-adenosylmethionine; met, methionine.
Scheme 2
Scheme 2. Multiple sequence alignment of six MTTases
Two from RimO_(E. coli K-12 and T. maritima DSMZ3109), two from MiaB (E. coli K- 12 and T. maritima DSMZ3109), one from MtaB (B. subtilis MGNA-001), and one from e-MtaB (M. musculus). The alignment was performed with ClustalW at the EBI site. Totally conserved residues are indicated by stars, and conserved cysteine residues are indicated by arrows. The three domains UPF0004, Radical-SAM, and TRAM are shown on the right.
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References

    1. Eisenstein O, Balcells D, Clot E. C-H Bond Activation in Transition Metal Species from a Computational Perspective. Chem. Rev. 2010;110:749–823. - PubMed
    1. Kovaleva EG, Lipscomb JD. Versatility of biological non-heme Fe(II) centers in oxygen activation reactions. Nature Chemical Biology. 2008;4:186–193. - PMC - PubMed
    1. Krebs C, Fujimori DG, Walsh CT, Bollinger JM. Non-heme Fe(IV)-oxo intermediates. Acc. Chem. Res. 2007;40:484–492. - PMC - PubMed
    1. Que L, Costas M, Mehn MP, Jensen MP. Dioxygen activation at mononuclear nonheme iron active sites: Enzymes, models, and intermediates. Chem. Rev. 2004;104:939–986. - PubMed
    1. Lippard SJ. Hydroxylation of C-H bonds at carboxylate-bridged diiron centres. Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences. 2005;363:861–877. - PubMed

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