Investigating Unfolded Proteins by Small-Angle X-Ray Scattering

Abstract

A clear description of the unfolded state is important for understanding protein folding/misfolding reactions. In addition to general ensemble-averaged properties, distributional residue-specific information is particularly necessary for identifying the molecular causes of many protein misfolding diseases. To this end, an anomalous SAXS (small angle X-ray scattering) technique was developed that provides residue-to-residue distance distribution information for unfolded proteins under physiological conditions. A peptide corresponding in sequence to the first helix of λ repressor was used for preliminary experiments with the proposed technique. Selenium and mercury labels were attached to the termini of the peptide and SAXS data of the labeled peptide were collected at the Argonne National Laboratory. End-to-end distance distribution for selenium-labeled peptide was obtained and the viability of the method was discussed based on experimental and simulation results.