Toshiyuki Tanaka Ph. D. Structural Biology

My research interests focus on the structure-function relationships of proteins involved in signal transduction. The goal of our research is to understand at the atomic level the mechanism of various biological processes including calcium signaling, the His-Asp phosphorelay system, and transcription regulation. We use multidimensional nuclear magnetic resonance (NMR) spectroscopy in conjunction with stable-isotope labeling of the macromolecules to study the structure, dynamics and kinetics of protein-protein, protein-DNA, and protein-drug complexes in solution. Detailed structural information of the protein interactions should provide new insights into the mechanism of biological machineries.

Much of our work in the past has been on Ca2+/recoverin and EnvZ phosphorelay signal transductions. Retinal recoverin contains a covalently attached myristoyl or related acyl group at its N-terminus and two Ca2+-binding sites. Ca2+ binding to myristoylated but not unmyristoylated recoverin induces its translocation to bilayer membranes, indicating that the myristoyl group plays an essential role in the read-out of calcium signals (calcium-myristoyl switch). We have determined both the Ca2+-free and -bound recoverin structures and revealed the switching mechanism in detail. The E. coli osmosensor, EnvZ is an integral membrane receptor, with histidine kinase activity in the cytoplasmic region. We recently determined the three-dimensional structure of the catalytic domain of EnvZ, and it revealed a novel protein kinase structure. Designs of new Ca2+-switching proteins and anti-bacterial drugs based on the determined structures are in progress.

Also of interest is the chromophore-protein interaction of chromoprotein antibiotics. The chromophore is very unstable, but is stabilized substantially by the specific and tight binding to its apoprotein. Their chromophore-binding structures and stabilization interactions are of great interest in connection with molecular recognition and protein transport. The structure determination of chromoprotein complexes as well as the site-directed mutagenetic experiments of apoproteins to understand the interaction mechanism is under way.

Selected Publications. Imajo, S., et al.; On the Conformation of Phe78 of a Chromoprotein Antibiotic, Neocarzinostatin. Bioorg. Med. Chem., 3, 429 - 436 (1995) : Tanaka, T., et al.; Sequestration of the Membrane-Targeting Myristoyl Group of Recoverin in the Calcium-Free State. Nature, 376, 444 - 447 (1995) : Zhang, M., et al.; Calcium-Induced Conformational Transition Revealed by the Solution Structure of Apo Calmodulin. Nature Struct. Biol., 2, 758 - 767 (1995) : Ames, J. B., et al.; Nuclear Magnetic Resonance Evidence for Ca2+-Induced Extrusion of the Myristoyl Group of Recoverin. J. Biol. Chem., 270, 30909 - 30913 (1995) : Iida, K., et al.; Absolute Configuration of C-1027 Chromophore. Tetrahedron Lett., 37, 4997 - 5000 (1996) : Ames, J. B., et al.; Molecular Mechanics of Calcium-Myristoyl Switches. Nature, 389, 198 - 202 (1997) : Osawa, M., et al.; Solution Structure of Calmodulin-W-7 Complex; The Basis of Diversity in Molecular Recognition. J. Mol. Biol., 276, 165 - 176 (1998) : Tanaka, T., et al.; Differential Isotope Labeling Strategy for Determining the Structure of Myristoylated Recoverin by NMR Spectroscopy. J. Biomol. NMR, 11, 135 - 152 (1998) : Tanaka, T., et al.; NMR Structure of the Histidine Kinase Domain of the E. coli Osmosensor EnvZ. Nature, 396, 88-92 (1998)