National Institutes of Health [GM110588 to M.A.S. and D.I.-R.]; California Metabolic Research Foundation. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]; The SSRL Structural Molecular Biology Program is supported by the Department of Energy Office of Biological and Environmental Research; National Institutes of Health; and the National Institute of General Medical Sciences [P41GM103393]. The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health or the National Institute of General Medical Sciences. Funding for open access charge: National Institutes of Health.
Nucleic Acids Research
Biosynthesis -- Molecular aspects
The universally conserved N 6-threonylcarbamoylade nosine (t 6 A) modification of tRNA is essential for translational fidelity. In bacteria, t 6 A biosynthesis starts with the TsaC/TsaC2-catalyzed synthesis of the intermediate threonylcarbamoyl adenylate (TC-AMP), followed by transfer of the threonylcarbamoyl (TC) moiety to adenine-37 of tRNA by the TC-transfer complex comprised of TsaB, TsaD and TsaE sub-units and possessing an ATPase activity required for multi-turnover of the t 6 A cycle. We report a 2.5-˚ A crystal structure of the T. maritima TC-transfer complex (TmTsaB 2 D 2 E 2) bound to Mg 2+-ATP in the AT-Pase site, and substrate analog carboxy-AMP in the TC-transfer site. Site directed mutagenesis results show that residues in the conserved Switch I and Switch II motifs of TsaE mediate the ATP hydrolysis-driven reactivation/reset step of the t 6 A cycle. Further , SAXS analysis of the TmTsaB 2 D 2-tRNA complex in solution reveals bound tRNA lodged in the TsaE binding cavity, confirming our previous biochemical data. Based on the crystal structure and molecular docking of TC-AMP and adenine-37 in the TC-transfer site, we propose a model for the mechanism of TC transfer by this universal biosynthetic system.
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Luthra, A., Paranagama, N., Swinehart, W., Bayooz, S., Phan, P., Quach, V., ... & Swairjo, M. A. (2019). Conformational communication mediates the reset step in t6A biosynthesis. Nucleic acids research.