Time resolved transient circular dichroism spectroscopy using synchrotron natural polarization.

François Auvray,Frédéric Jamme,Jonathan D Hirst,David Dennetiere,Alexandre Giuliani,Frank Wien,Bastien Nay,François Polack,Matthieu Réfrégiers,Bruno Lagarde,Séverine Zirah,Claude Menneglier

doi:10.1063/1.5120346

Abstract

Ultraviolet (UV) synchrotron radiation circular dichroism (SRCD) spectroscopy has made an important contribution to the determination and understanding of the structure of bio-molecules. In this paper, we report an innovative approach that we term time-resolved SRCD (tr-SRCD), which overcomes the limitations of current broadband UV SRCD setups. This technique allows accessing ultrafast time scales (down to nanoseconds), previously measurable only by other methods, such as infrared (IR), nuclear magnetic resonance (NMR), fluorescence and absorbance spectroscopies, and small angle X-ray scattering (SAXS). The tr-SRCD setup takes advantage of the natural polarization of the synchrotron radiation emitted by a bending magnet to record broadband UV CD faster than any current SRCD setup, improving the acquisition speed from 10 mHz to 130 Hz and the accessible temporal resolution by several orders of magnitude. We illustrate the new approach by following the isomer concentration changes of an azopeptide after a photoisomerization. This breakthrough in SRCD spectroscopy opens up a wide range of potential applications to the detailed characterization of biological processes, such as protein folding and protein-ligand binding.

Highlights

Circular dichroism (CD) is an optical property of molecules having chiral structure(s) and/or spatially oriented arrays of chromophores
Ultraviolet (UV) synchrotron radiation circular dichroism (SRCD) spectroscopy has made an important contribution to the determination and understanding of the structure of bio-molecules
We report an innovative approach that we term time-resolved SRCD, which overcomes the limitations of current broadband UV SRCD setups

Summary

Introduction

Circular dichroism (CD) is an optical property of molecules having chiral structure(s) and/or spatially oriented arrays of chromophores. It manifests itself as a difference in absorption for left- and right-circularly polarized light. In the ultraviolet (UV) range, this feature has been exploited for decades for the characterization of organic molecules, materials with supramolecular chirality, and in protein conformation determination, where there are distinctive spectral signatures for each secondary structure type, i.e., a-helices and b-sheets.[1] CD spectroscopy is an important biophysical tool for characterizing native and modified proteins. Structural and kinetics studies of protein folding, using time-resolved approaches, are providing crucial insights at the molecular level into the etiology of these diseases

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