TY - JOUR
T1 - Structural basis for non-radical catalysis by TsrM, a radical SAM methylase
AU - Knox, Hayley L.
AU - Chen, Percival Yang Ting
AU - Blaszczyk, Anthony J.
AU - Mukherjee, Arnab
AU - Grove, Tyler L.
AU - Schwalm, Erica L.
AU - Wang, Bo
AU - Drennan, Catherine L.
AU - Booker, Squire J.
N1 - Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer Nature America, Inc.
PY - 2021/4
Y1 - 2021/4
N2 - Tryptophan 2C methyltransferase (TsrM) methylates C2 of the indole ring of l-tryptophan during biosynthesis of the quinaldic acid moiety of thiostrepton. TsrM is annotated as a cobalamin-dependent radical S-adenosylmethionine (SAM) methylase; however, TsrM does not reductively cleave SAM to the universal 5ʹ-deoxyadenosyl 5ʹ-radical intermediate, a hallmark of radical SAM (RS) enzymes. Herein, we report structures of TsrM from Kitasatospora setae, which are the first structures of a cobalamin-dependent radical SAM methylase. Unexpectedly, the structures show an essential arginine residue that resides in the proximal coordination sphere of the cobalamin cofactor, and a [4Fe–4S] cluster that is ligated by a glutamyl residue and three cysteines in a canonical CXXXCXXC RS motif. Structures in the presence of substrates suggest a substrate-assisted mechanism of catalysis, wherein the carboxylate group of SAM serves as a general base to deprotonate N1 of the tryptophan substrate, facilitating the formation of a C2 carbanion. [Figure not available: see fulltext.]
AB - Tryptophan 2C methyltransferase (TsrM) methylates C2 of the indole ring of l-tryptophan during biosynthesis of the quinaldic acid moiety of thiostrepton. TsrM is annotated as a cobalamin-dependent radical S-adenosylmethionine (SAM) methylase; however, TsrM does not reductively cleave SAM to the universal 5ʹ-deoxyadenosyl 5ʹ-radical intermediate, a hallmark of radical SAM (RS) enzymes. Herein, we report structures of TsrM from Kitasatospora setae, which are the first structures of a cobalamin-dependent radical SAM methylase. Unexpectedly, the structures show an essential arginine residue that resides in the proximal coordination sphere of the cobalamin cofactor, and a [4Fe–4S] cluster that is ligated by a glutamyl residue and three cysteines in a canonical CXXXCXXC RS motif. Structures in the presence of substrates suggest a substrate-assisted mechanism of catalysis, wherein the carboxylate group of SAM serves as a general base to deprotonate N1 of the tryptophan substrate, facilitating the formation of a C2 carbanion. [Figure not available: see fulltext.]
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U2 - 10.1038/s41589-020-00717-y
DO - 10.1038/s41589-020-00717-y
M3 - Article
C2 - 33462497
AN - SCOPUS:85100121521
SN - 1552-4450
VL - 17
SP - 485
EP - 491
JO - Nature Chemical Biology
JF - Nature Chemical Biology
IS - 4
ER -