MUTATIONAL ACTIVATION OF CYTOKINE ACTIVITY 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. We have been working with human aminoacyl-tRNA synthetases, enzymes catalyze the first step of protein biosynthesis. However some of those enzymes have cell-signaling activities (e.g. cell migration, angiogenesis, and etc). Tyrosyl-tRNA synthetase (TyrRS) is one of them. TyrRS can be split into two fragments (mini-TyrRS and C-TyrRS), and both have cell- signaling activities. Yet the full-length TyrRS is inactive in cell- signaling. The hypothesis is that the key residues for the cytokine activities of both mini-TyrRS and C-TyrRS are mutually masked in the full- length protein. We have solved the crystal structure of the two fragments (but not the full-length), and has identified a residue (Y341) that might be critical for tethering the two fragments together in the full-length protein. Remarkably, the full-length Y341A mutant has gained cytokine activity in our two independent angiogenesis assays, presumably by opening up the full-length protein. This result suggests that our proposed mechanism for cytokine activation may be real. In order to confirm this, doing SAXS on both the native TyrRS and the Y341A mutant can be very helpful. We expect to see the mutant has a more opened structure with larger radius of gyration. In addition, it will be very cool if a low resolution envelop of the molecule can be generated from the SAXS data to show that the wild type is more closed, and the mutant is more open. Since we have the crystal structures of the two components, it should help in generating such an envelop model.