Report

Energy Transduction on the Nanosecond Time Scale: Early Structural Events in a Xanthopsin Photocycle

+ See all authors and affiliations

Science  20 Mar 1998:
Vol. 279, Issue 5358, pp. 1946-1950
DOI: 10.1126/science.279.5358.1946

You are currently viewing the abstract.

View Full Text

Abstract

Photoactive yellow protein (PYP) is a member of the xanthopsin family of eubacterial blue-light photoreceptors. On absorption of light, PYP enters a photocycle that ultimately transduces the energy contained in a light signal into an altered biological response. Nanosecond time-resolved x-ray crystallography was used to determine the structure of the short-lived, red-shifted, intermediate state denoted [pR], which develops within 1 nanosecond after photoelectronic excitation of the chromophore of PYP by absorption of light. The resulting structural model demonstrates that the [pR] state possesses the cis conformation of the 4-hydroxyl cinnamic thioester chromophore, and that the process oftrans to cis isomerization is accompanied by the specific formation of new hydrogen bonds that replace those broken upon excitation of the chromophore. Regions of flexibility that compose the chromophore-binding pocket serve to lower the activation energy barrier between the dark state, denoted pG, and [pR], and help initiate entrance into the photocycle. Direct structural evidence is provided for the initial processes of transduction of light energy, which ultimately translate into a physiological signal.

  • * To whom correspondence should be addressed. E-mail: moffat{at}cars.uchicago.edu

View Full Text