Professor Keith Moffat
Department of Biochemistry & Molecular Biology
The University of Chicago
Chicago, IL

Wednesday, May 18, 2005
11:00 am (CT)
3269 Beckman Institute

Abstract

Certain signalling photoreceptors harness the energy in a photon and use it to generate a structural signal that ultimately alters an aspect of biological behavior such as swimming in a bacterium or phototropism in plants. How is this achieved, at the atomic level? We conduct pump-probe experiments on single crystals of photoreceptors, in which a structural reaction is initiated by a laser pulse - the pump - and followed by a brief, intense, polychromatic X-ray pulse - the probe. The resultant time-dependent diffraction patterns yield time-dependent difference electron density maps that display how the average structure changes with time, over a time range from nsec to sec. These maps can in turn be analyzed to yield a candidate chemical kinetic mechanism (if one exists) and the time-independent structures of the short-lived intermediates that populate the mechanism. These ideas will be illustrated by experiments that explore the photocycle of the "simple" bacterial blue light photoreceptor, photoactive yellow protein, and other signalling proteins of the PAS domain family.