Question

Why is a protein crystal necessary to resolve protein structures via X-ray? (as opposed to a solution of molecules? As opposed to a single protein that say is completely static?)

Answer 1

Protein X-ray crystallography is a technique used to obtain the three-dimensional structure of a particular protein by x-ray diffraction of its crystallized form. This three dimensional structure is crucial to determining a protein's functionality. Making crystals creates a lattice in which this technique aligns millions of proteins molecules together to make the data collection more sensitive. It's like getting a stack of papers, measuring the width with a ruler, and dividing that length with the number of pages to determine the width of one piece of paper. By this averaging technique, the noise level gets reduced and the signal to noise ratio increases. The specificity of the protein's active sites and binding sites is completely dependent on the protein's precise conformation. X-ray crystallography can reveal the precise three-dimensional positions of most atoms in a protein molecule because x-rays and covalent bonds have similar wavelength, and therefore currently provides the best visualization of protein structure.