Crystallographic structure of a photoreceptor protein at 2.4 A resolution.
The first essential step in protein photoreception is the capture and storage of energy from a photon. We have recently identified and isolated, from the purple photoautotrophic bacterium, Ectothiorhodospira halophila, a 13,000-dalton photoactive yellow protein (PYP) that has a photocycle with kinetics similar to sensory rhodopsin and a very high quantum efficiency. To study the structural chemistry of protein photoreception, we determined, refined, and analyzed the crystallographic structure of PYP at 2.4 A resolution and report here that it is composed of two perpendicular antiparallel beta-sheets that enclose the chromophore. Each of the 10 beta-strands of PYP is connected directly to its nearest neighbor with +1 topology. Globally, an asymmetric distribution of side chains places aromatic and acidic side chains in an ellipsoidal band around the chromophore with a cluster of basic side chains on one side. Locally, the electron density maps place an internal lysine and the chromophore in an apparent Schiff base linkage stabilized by a buried glutamate and a tyrosine side chain. To our knowledge, the atomic resolution structure of a protein with a reversible photoisomerization has not been reported previously. Furthermore, PYP may also represent a class of proteins that bind conjugated molecules and interact with a secondary receptor system.
Department of Molecular Biology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
D E
DE
McRee
J A
JA
Tainer
T E
TE
Meyer
J
J
Van Beeumen
M A
MA
Cusanovich
E D
ED
Getzoff
D001426:Bacterial Proteins / Q000302:isolation & purification; D002841:Chromatiaceae / Q000378:metabolism*; D008958:Models, Molecular; D020283:Photoreceptors, Microbial; D011487:Protein Conformation; D014961:X-Ray Diffraction
D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria