Measuring Intramolecular Distance Distributions in Proteins by Anomalous Small-Angle X-ray Scattering

Substrate-binding proteins (SBPs) mediate the uptake of nutrients into a bacterial cell, which is known to critically depend on the conformational state of the proteins. Anomalous small-angle x-ray scattering (ASAXS) applied to biological macromolecules site-specifically labeled with small (~1.4 nm in diameter) gold nanoparticles provides a powerful molecular ruler. The ASAXS ruler approach gives precise and absolute information on the full distance distribution of the gold labels with Ångström-precision. However, its potential to reveal conformational states of proteins has not been demonstrated yet. During our previous beamtime (LS-2945) we successfully measured the distances between pairs of gold labels attached to two maltose binding protein (MalE) mutants. We want to now build on these very promising results and continue this project to demonstrate the full potential of the technology and also monitor the full ensemble involved in the conformational changes.