Phone: (310) 206-8830
Fax: (310) 794-2144
Stein Eye Institute
100 Stein Plaza, Room BH-973
Los Angeles CA, 90095
Retinal Photoreceptor Membrane Structure and Function
Dr. Hubbell's research is focused on understanding the relationship between the molecular structure of a protein and the conformational changes that control its function. Of particular interest are membrane proteins that behave as "molecular switches", i.e., proteins whose structures are switched to an active state by a physical or chemical signal. A primary example under study is light-activated rhodopsin, the visual pigment in photoreceptor cells of the retina. The goal is to elucidate the structure of rhodopsin, the mechanism of the molecular switch, and the regulation of this switch by associated proteins, transducin and arrestin. Recently, his research has broadened to include structure/function relationships in water-soluble proteins such as the lens protein a-crystallin and the family of retinoid carrying proteins that transport vitamin A throughout photoreceptor cells.
To investigate these proteins, Dr. Hubbell's laboratory has developed the technique of site-directed spin labeling (SDSL), a novel and powerful approach to the exploration of protein structure and dynamics. By changing the genetic code, a specific attachment point in the protein is created for a nitroxide spin label probe. Analysis of the electron paramagnetic resonance (EPR) spectrum of the spin label provides a wealth of information about the local environment in the protein. With a sufficiently large set of labeled proteins, global information on structure is obtained, and most importantly, changes in the structure during function can be followed in real time.
Using SDSL, Dr. Hubbell's laboratory, in collaboration with colleagues at the Massachusetts Institute of Technology, has developed a topological map of rhodopsin and followed the detailed structural changes that take place upon activation by a single photon of light. Determining such molecular details is essential to understanding the underlying causes of retinal diseases, like retinitis pigmentosa.
Farrens D, Altenbach C, Yang K, Hubbell W, Khorana HG. Requirement of rigid-body motion of transmembrane helices for light activation of rhodopsin. Science 1996;274:768-70.
Gross A, Columbus L, Hideg K, Altenbach C, Hubbell W. The structure of the KcsA potassium channel from Streptomyces lividans: A site-directed spin labeling study of the second transmembrane segment. Biochemistry 1999;38:10324-35.
Hubbell W, Cafiso D, Altenbach C. Monitoring conformational changes with site-directed spin labeling. Nat Struct Biol 2000;7:735-9.
Columbus L, Kalai T, Jeko J, Hideg K, Hubbell W. Molecular motion of spin labeled side chains in a-helices: Analysis by variation of side chain structure. Biochemistry 2001;40:3828-46.
Altenbach C, Cai K, Klein-Seetharaman J, Khorana HG, Hubbell W. Structure and function in rhodopsin: Mapping light-dependent changes in distance between residue 65 in Helix TM1 and residues in the sequence 306-319 at the cytoplasmic end of helix TM7 and in helix H8. Biochemistry (In Press).
National Eye Institute: Core Grant for Vision Research, 3/1/99-2/28/04
National Eye Institute: Molecular Basis of Membrane Excitation, 5/1/00-4/30/05
Research to Prevent Blindness: Senior Scientific Investigator Award, 1/1/00-12/31/05
U.S. Army Research Office: Advanced Development of Electron Spin Labels as High-Resolution Sensors of Protein Structure and Conformational Switching, 5/1/01-4/30/03