SOLUTION STRUCTURE OF A HUMAN AMINOACYL-TRNA SYNTHETASE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tyrosyl-tRNA synthetase (TyrRS) is one of the human aminoacyl-tRNA synthetases that catalyze the first step of protein biosynthesis and are involved in cell-signaling activities such as cell migration and angiogenesis. We have solved the crystal structure of the isolated N-terminal and C-terminal domains individually, and have recently conducted solution x-ray scattering experiments at SSRL on the wild type enzyme as well as Y341A mutant to obtain the solution structure of the full-length enzyme. The wild type full length protein is inactive in cell signaling while Y341A mutant has active cytokine activity, implying the Y341 may have an open structure, compared to that of the wild type enzyme. We obtained the radii of gyration 47 and 50 ¿ for the wild type and mutant enzyme, respectively by Guinier plots. The electron pair distance distribution function has two mixima, one around 30 ¿ and the other around 60 ¿. The first peak is substantially lower in the case of the mutant, and this is accompanied by the increase in the distribution in a larger inter-distances, resulting in the increase in the maximum dimension (Dmax) from 150 ¿ to approximately 160 ¿. These results confirm that the mutant has a more open structure, strongly supporting our hypothesis that the domain closure between N- and C-terminal domains plays a key role in the regulation of the cytokine activity. We are in the process of building a low-resolution structural envelope based on the solution scattering data in an effort to fit the crystal domain structures into the envelope.