Electron Microscopy of Thin Protein Crystals from Vapour Diffusion ‘Hanging Drops’ Provides Structural Information at Intermediate Resolution

Abstract

Electron crystallography has emerged as a powerful method for the determination of molecular structures at intermediate to high spatial resolutions (3 — 20 A). Together with direct imaging by high resolution electron microscopy this technique provide an excellent tool for protein crystal analysis. However, application of these methods depends on the availability of relatively large (micrometre size), well-ordered and thin crystalline arrays of the protein molecules. One source of such crystals is that from vapour diffusion ‘hanging drops’ which have been set up in order to grow crystals suitable for X-ray diffraction. Crystals grown under these conditions are sometimes not suitable for X-ray analysis but when harvested onto an electron microscope grid prove to be sufficiently thin for analysis by electron microscopy.