TsrM catalyzes the methylation of C2 in Ltryptophan (Trp). This reaction is the first step in the biosynthesis of the quinaldic acid moiety of the thiopeptide antibiotic thiostrepton, which exhibits potent activity against Gram-positive pathogens. TsrM is a member of the radical S-adenosylmethionine (SAM) superfamily of enzymes, but does not catalyze formation of 5'-deoxyadenosin-5'-yl or any other SAM-derived radical. In addition to a [4Fe-4S] cluster, TsrM contains a cobalamin cofactor that serves as an intermediate methyl carrier in its reaction. However, how this cofactor donates a methyl moiety to the Trp substrate is unknown. Here, we show that an unmodified N1 position of Trp is important for turnover and that 1-thia-Trp and 1-oxa-Trp serve as competitive inhibitors. We also show that β-cyclopropyl-Trp undergoes C2 methylation in the absence of cyclopropyl ringopening, disfavoring mechanisms that involve unpaired electron density at C3 of the indole ring. Moreover, we show that all other indole-substituted analogs of Trp undergo methylation at varying but measurable rates, and that the analog 7-aza-Trp - which is expected to temper the nucleophilicity of C2 in Trp-is a very poor substrate. Lastly, no formation of cob(II)alamin or substrate radicals is observed during the reaction with Trp or any molecule within a tested panel of Trp analogs. In summary, our results are most consistent with a mechanism that involves two polar nucleophilic displacements, the second of which requires deprotonation of the indole nitrogen in Trp during its attack on methylcobalamin.
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Publication date: Available online 4 January 2018 Source: European Journal of Radiology Author(s): Peiyao Zhang, Jing Wang, Qin Xu, Zhen...
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Publication date: March 2017 Source: Free Radical Biology and Medicine, Volume 104 from #AlexandrosSfakianakis via Alexandros G.Sfak...
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BACKGROUND AND PURPOSE: Dengue is a common arboviral disease, which uncommonly involves the brain. There has been a recent surge in dengu...
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Linked Article: Maintz et al. Br J Dermatol 2017; 176:481–487 . from #AlexandrosSfakianakis via Alexandros G.Sfakianakis on Inoreader h...
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Publication date: Available online 28 February 2018 Source: Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology Author(s): Mo...
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