Macromolecular neutron crystallography at the Protein Crystallography Station (PCS)

Abstract

The Protein Crystallography Station (PCS) at Los Alamos Neutron Science Center is a high-performance beamline that forms the core of a capability for neutron macromolecular structure and function determination. Neutron diffraction is a powerful technique for locating H atoms and can therefore provide unique information about how biological macromolecules function and interact with each other and smaller molecules. Users of the PCS have access to neutron beam time, deuteration facilities, the expression of proteins and the synthesis of substrates with stable isotopes and also support for data reduction and structure analysis. The beamline exploits the pulsed nature of spallation neutrons and a large electronic detector in order to collect wavelength-resolved Laue patterns using all available neutrons in the white beam. The PCS user facility is described and highlights from the user program are presented.

Figure 1

PCS user program statistics.

Figure 2

OMIT F _o − F _c (red, contoured at the 2σ level) and 2F _o − F _c (green, contoured at the 1.6σ level) nuclear density maps for α₁His45 (a) and β₁His63 (b) residues that demonstrate how the protonation states for neutral and charged histidines, respectively, were determined. Peaks in OMIT F _o − F _c maps correspond to D atoms.

Figure 3

Cyclic and linear glucose substrates binding in XI-Cd-CyclicSugar and XI-Ni-LinearSugar, respectively, and the important active-site residues His54, Lys813 and Lys289. Neutron scattering density shown is contoured at the 1.6σ level.

Figure 4

Neutron structure of HCA II. (a) Active-site residues and water network of HCA II shown in ball-and-stick representation; 2F _o − F _c nuclear map in orange, contoured at 1.5σ. (b) Tyr7 is deprotonated and is a hydrogen-bond acceptor of W3a; 2F _o − F _c positive nuclear map in orange, negative map in green, both contoured at 1.5σ.