Protein crystallography resource at neutron research center for imaging proteins

Understanding the structure of proteins and polymers is also key to understanding the messages encoded in human DNA.

At the facility, researchers place a sample of a material in the path of a beam of neutrons. Neutrons in the beam scatter when they interact with the atoms in the sample. A detector behind the sample records how the neutrons were scattered and renders a two-dimensional, black-and-white stippled image— a crude mandala of sorts. This diffraction pattern is manipulated and then analyzed by a computer to reveal the 3-D structure of the sample. The computer analysis accurately portrays the relative distances between the atoms that make up the structure, the lengths and angles of the bonds between atoms in the structure and the position and location of each hydrogen atom in the structure.

The neutron-diffraction-imaging process is a little like making and interpreting an X-ray image. In fact, structural biologists use X-ray diffraction to make images of organic molecules. But unlike X-ray diffraction, which is "blind" to hydrogen, neutron diffraction yields accurate information about hydrogen atoms contained in a structure. Being able to see and understand hydrogen atoms in a polymer, like DNA, or in a protein segment is key to understanding how the protein or polymer functions. Hydrogen is key to many internal and external reactions of proteins with other biological chemicals. Hydrogen atoms act like tiny switches to activate a chemical or to keep it in "standby" mode. Because ordinary hydrogen can be substituted by deuterium—a stable isotope of hydrogen that has an extra neutron in its nucleus—and because the neutron scattering data can distinguish between hydrogen and deuterium atoms, scientists will be able to get a better idea of which hydrogen atoms are actually switches and which are simply chemical place- holders in a molecule.

Moreover, because neutron diffraction can see hydrogen, researchers will be able to better understand the role that water (two hydrogen atoms bound to an oxygen atom) plays in proteins and polymers. In some cases, water molecules are simply a structural building block. In others, water arranges itself into a funnel configuration that allows other chemicals to move from one area to another. Understanding the role of water in biological chemicals is a key field of study for some Los Alamos researchers.