CRYSTALLOGRAPHIC EVIDENCE OF A LARGE LIGAND-INDUCED CONFORMATIONAL CHANGE BETWEEN THE TWO DOMAINS OF THE GLUTAMINE-BINDING PROTEIN. Yuh-Ju Sun¹, A-Yen. Hsin¹, Chien Ho², Bi-Cheng Wang^3, Chwan-Deng Hsiao^l, Crystallographic Laboratory, Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, 11529¹, Department of Biological Sciences Carnegie Mellon University, Pittsburgh, PA 15213, USA^2, Departments of Biochemistry and Molecular Biology University of Georgia, Athens, GA 30602-7229

The large-scale movement of rigid globular domains has been found in many proteins. Such conformational changes have been found to be responsible for specific functions, such as ligand binding, catalysis, and recognition by other biomolecules. Among these, bacterial periplasmic binding proteins involved in ligand transport across cell membrane and/or chemotaxis, can be used as probes for understanding the mechanism of the movement. The three-dimensional structures of a periplasmic binding protein from Escherichia coli, "glutamine-binding protein"(GlnBP) without and with ligand have been determined by X-ray crystallographic methods. They are composed of two globular domains which are held together by two short connecting hinges. The two domains are far apart in the,GlnBP unliganded structure, in "open" conformation, but close together in the GlnBP-Gln liganded structure, in "close" conformation. This large conformational change between the two domains is a consequence of approximately 48deg. bending of small domain through the connecting hinges.