Preliminary Characterization of Crystals

To determine whether crystals of macromolecules are suitable for crystallographic studies, they must be fully characterized. Characterrzatron is intended to answer many important questions about the crystals. Do they diffract X-rays? Do they diffract to a suitable resolution? Are they stable in the X-ray beam? What is their overall symmetry? What are the dimensions of their repeating unit? How many protein molecules are in that repeating unit? The answer to these questions is important to ensure a successful structure determination. There is nothing more frustrating than growing large beautiful crystals that do not diffract X-rays, diffract poorly, have a large repeating unit, or are unstable in the X-ray beam. Crystals that diffract to less than 3.5-� resolution may be useless for answering most structural questions because of the inability to trace unambiguously the polypeptide chain and define clearly the side chains at such resolutions. Large repeating units (with any dimension >250 �) and unstable crystals, on the other hand, complicate data acquisition from most laboratory equipment.