X-ray crystallography is a technique togenerate the three-dimensional structures of proteins at an atomic level andunderstand their functions from its crystallised form. There are three main componentsneeded to complete an x-ray crystallography analysis – a purified sample athigh concentration which is crystallised, an X-ray source and a detector wherethe resulting diffraction patterns are processed.
Why use X-rays?Theresolution of an image in any form of microscopy depends on the wavelength ofelectromagnetic radiation used. Light microscopy (where the range ofwavelengths is 380-750nm) is used to see individual cells and sub-cellularorganelles. Electron microscopy (where the wavelength is approximately 10nm) isused to see cellular architecture and the shapes of large protein molecules.
Therefore,to see proteins at an atomic level, electromagnetic radiation of around 0.1 nmshould be used – this corresponds to the wavelength of X-rays. 1Why do we need a crystal?The diffractionfrom a single molecule is too weak to be measured therefore the proteins arecrystallised. The diffraction of a crystal is measurable as there are multiplecopies within them. Typical protein cells crystals are about 0.2mm in size butusable crystals have been reported from tens of microns to a few millimetres.2