The aminoacyl-tRNA synthetases comprise a family of twenty enzymes that are essential to every living organism. Each enzyme recognizes a single cognate amino acid and covalently attaches it to the correct tRNA. The """"""""charged"""""""" tRNA then transfers the amino acid at the ribosome for specific incorporation into the growing polypeptide chain. The fidelity of protein synthesis is completely dependent on accurate substrate recognition by the tRNA synthetases. Some tRNA synthetases have developed editing mechanisms to correct misactivated amino acids. This proofreading step increases fidelity by as much as two orders of magnitude. However, little is known about the recognition of misactivated amino acids or the hydrolytic cleavage mechanism. This proposal outlines an interdisciplinary research plan combining computational, biochemical, and molecular biology approaches to identify the editing active sites and elucidate the molecular mechanism of the tRNA-dcpendent editing activity using leucyl (Leu-) tRNA synthetase as a novel model. The leucine enzyme editing activities occur by distinct species-specific mechanisms. The E. coli enzyme exhibits a clear """"""""post-transfer"""""""" activity that requires transfer of the amino acid to the tRNA for editing, while the yeast enzyme functions by a """"""""pre-transfer"""""""" mechanism that hydrolyzes misactivated adenylate intermediates. Emerging hypotheses suggest that the pre- and post-transfer editing active sites may be distinct. Preliminary data are described that identifies the post-transfer editing active site. Subsequent proposed work in Specific Aim I will map and delineate the molecular determinants of this editing active site in E. coli Leu-tRNA synthetase. A series of experiments are also outlined to identify and characterize the pre-transfer editing active site using yeast Leu-tRNA synthetase.
In Specific Aim II, a strategic plan is presented to determine which noncognate amino acids threaten the fidelity of Leu-tRNA synthetases such that this enzyme maintains an editing active site. Finally, complementation experiments will test the physiological effects of editing-defective tRNA synthetases on cell viability. A detailed understanding of the tRNA synthetase editing mechanism, particularly those that are species-specific, will benefit ongoing pharmaceutical research that is actively exploring tRNA synthetases as a target for antibiotic development. It will also enable reengineering of tRNA synthetases to activate alternative amino acids for incorporation into custom-designed proteins. These novel proteins could be used as therapeutics or important tools in medicinal and technological applications.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Microbial Physiology and Genetics Subcommittee 2 (MBC)
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Rhoades, Marcus M
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University of Houston
Schools of Arts and Sciences
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Zhao, Hanchao; Palencia, Andres; Seiradake, Elena et al. (2015) Analysis of the Resistance Mechanism of a Benzoxaborole Inhibitor Reveals Insight into the Leucyl-tRNA Synthetase Editing Mechanism. ACS Chem Biol 10:2277-85
Pang, Yan Ling Joy; Poruri, Kiranmai; Martinis, Susan A (2014) tRNA synthetase: tRNA aminoacylation and beyond. Wiley Interdiscip Rev RNA 5:461-80
Li, Li; Martinis, Susan A; Luthey-Schulten, Zaida (2013) Capture and quality control mechanisms for adenosine-5'-triphosphate binding. J Am Chem Soc 135:6047-55
Li, Li; Palencia, Andrés; Lukk, Tiit et al. (2013) Leucyl-tRNA synthetase editing domain functions as a molecular rheostat to control codon ambiguity in Mycoplasma pathogens. Proc Natl Acad Sci U S A 110:3817-22
Boniecki, Michal T; Martinis, Susan A (2012) Coordination of tRNA synthetase active sites for chemical fidelity. J Biol Chem 287:11285-9
Sarkar, Jaya; Poruri, Kiranmai; Boniecki, Michal T et al. (2012) Yeast mitochondrial leucyl-tRNA synthetase CP1 domain has functionally diverged to accommodate RNA splicing at expense of hydrolytic editing. J Biol Chem 287:14772-81
Palencia, Andres; Crepin, Thibaut; Vu, Michael T et al. (2012) Structural dynamics of the aminoacylation and proofreading functional cycle of bacterial leucyl-tRNA synthetase. Nat Struct Mol Biol 19:677-84
Sarkar, Jaya; Martinis, Susan A (2011) Amino-acid-dependent shift in tRNA synthetase editing mechanisms. J Am Chem Soc 133:18510-3
Sarkar, Jaya; Mao, Weimin; Lincecum Jr, Tommie L et al. (2011) Characterization of benzoxaborole-based antifungal resistance mutations demonstrates that editing depends on electrostatic stabilization of the leucyl-tRNA synthetase editing cap. FEBS Lett 585:2986-91
Li, Li; Boniecki, Michal T; Jaffe, Jacob D et al. (2011) Naturally occurring aminoacyl-tRNA synthetases editing-domain mutations that cause mistranslation in Mycoplasma parasites. Proc Natl Acad Sci U S A 108:9378-83

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