© 2004 National Academies of Science

Comparison of three water sites captured under various conditions demonstrates the power of cryo-neutron crystallography. Associated water molecules W1 (left), W6 (center), and W75 (right), were imaged by neutron crystallography at 15K (top) and 293K (middle) and by X-ray crystallography at 110K. Note the changing positions of hydrogen atoms in all three structures, and the extra D2O position near W6 revealed at 15K. (Reprinted with permission from M.P. Blakeley et al., Proc Natl Acad Sci, 101:16405–10, 2004.)

X-ray crystallography has long been the method of choice for obtaining atomic-resolution protein structures, but it doesn't provide the whole picture. Hydrogen atoms, particularly labile hydrogens that interact with solvent, are often lost in the noise. "It is exceedingly difficult – usually impossible – to see a single hydrogen atom with X-rays," says Dean Myles, a crystallographer at the Oak Ridge...

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