Reaction: S-adenosyl-L-methionine + L-tryptophan = S-adenosyl-L-homocysteine + 2-methyl-L-tryptophan (overall reaction)
(1a) methylcob(III)alamin + L-tryptophan = cob(I)alamin + 2-methyl-L-tryptophan
(1b) S-adenosyl-L-methionine + cob(I)alamin = S-adenosyl-L-homocysteine + methylcob(III)alamin
Other name(s): tsrM (gene name); tryptophan 2-methyltransferase; S-adenosylmethionine:tryptophan 2-methyltransferase
Systematic name: S-adenosyl-L-methionine:L-tryptophan 2-C-methyltransferase
Comments: The enzyme, characterized from the bacterium Streptomyces laurentii, is involved in thiostrepton biosynthesis. It is a radical SAM enzyme that contains a [4Fe-4S] center and a methylcob(III)alamin cofactor. It has an exceptional reaction mechanism as the S-adenosyl-L-methionine (SAM) is not bound to the [4Fe-4S] center and does not produce a 5'-deoxyadenosyl radical but instead is believed to be involved in binding of the L-tryptophan substrate. After transfer of the methyl group from methylcob(III)alaminIn a methyl transfer from SAM to the generated cob(I)alamin takes place, preparing the enzyme for the next catalytic cycle. The original methyl group configuration is preserved.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 126626-83-3
References:
1. Frenzel, T., Zhou, P. and Floss, H.G. Formation of 2-methyltryptophan in the biosynthesis of thiostrepton: isolation of S-adenosylmethionine:tryptophan 2-methyltransferase. Arch. Biochem. Biophys. 278 (1990) 35-40. [PMID: 2321967]
2. Pierre, S., Guillot, A., Benjdia, A., Sandstrom, C., Langella, P. and Berteau, O. Thiostrepton tryptophan methyltransferase expands the chemistry of radical SAM enzymes. Nat. Chem. Biol. 8 (2012) 957-959. [PMID: 23064318]
3. Blaszczyk, A.J., Silakov, A., Zhang, B., Maiocco, S.J., Lanz, N.D., Kelly, W.L., Elliott, S.J., Krebs, C. and Booker, S.J. Spectroscopic and electrochemical characterization of the ion-sulfur and cobalamin cofactors of TsrM, an unusual radical S-adenosylmethionine methylase. J. Am. Chem. Soc. 138 (2016) 3416-3426. [PMID: 26841310]
4. Blaszczyk, A.J., Wang, B., Silakov, A., Ho, J.V. and Booker, S.J. Efficient methylation of C2 in L-tryptophan by the cobalamin-dependent radical S-adenosylmethionine methylase TsrM requires an unmodified N1 amine. J. Biol. Chem. 292 (2017) 15456-15467. [PMID: 28747433]
5. Knox, H.L., Chen, P.Y., Blaszczyk, A.J., Mukherjee, A., Grove, T.L., Schwalm, E.L., Wang, B., Drennan, C.L. and Booker, S.J. Structural basis for non-radical catalysis by TsrM, a radical SAM methylase. Nat. Chem. Biol. 17 (2021) 485-491. [PMID: 33462497]