TCBG Seminar

Why does a photoreceptor protein need proton transfers for activation?

Professor Aihua Xie
Department of Physics
Oklahoma State University
Stillwater, Oklahoma

Monday, March 5, 2001
3:00 pm (CT)
3269 Beckman Institute


Light-driven proton transfer is not only essential for biological energy transduction, but also indispensable for photoreceptor activation in biological signal transduction. We study the functional mechanism of photoactive yellow protein (PYP), a blue light photoreceptor, as a model system. Unlike rhodopsins for animal and bacterial vision, PYP is a small (125aa) water soluble protein, and does not contain a positively charged retinal, but a negatively charged p-coumeric acid as the chromophore for light detection. We will present structural, kinetic, and energetic evidence on and a molecular mechanism for PYP activation based on time-resolved Fourier transformed infrared (FTIR) spectroscopy in combination with site-specific mutation and electrostatic energy calculations. We will show that formation of a new buried charge via light-induced intramolecular proton transfer drives a large- amplitude protein quake, resulting in PYP activation. In addition, we will demonstrate that the large structural developments for PYP activation in solution are not present in crystaline PYP molecules and will discuss what we can and cannot learn from time-resolved X-crystallography of proteins.

Tea and coffee will be served in R3151 Beckman Institute at 2:15pm.

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