Section 8.1.8.1. Atomic and ultra high resolution macromolecular crystallography

The use of high SR intensity, cryo-freezing of a protein crystal to largely overcome radiation damage and sensitive, automatic area detectors (CCDs and/or image plates) is allowing diffraction data to be recorded at resolutions equivalent to smaller molecule (chemical) crystallography. In a growing number of protein crystal structure studies, atomic resolution (1.2 Å or better) is achievable (Dauter et al., 1997). The `X-ray data to parameter' ratio can be favourable enough for single and double bonds, e.g. in carboxyl side chains, to be resolved [Fig. 8.1.8.1; Deacon et al. (1997) for concanavalin A at 0.94 Å resolution]. Along with this bond distance precision, one can see the reactive proton directly. This approach complements H/D exchange neutron diffraction studies. Neutron studies have recently expanded in scope by employing Laue geometry in a synergistic development with SR Laue diffraction (Helliwell & Wilkinson, 1994; Helliwell, 1997b; Habash et al., 1997, 2000). The scope and accuracy of protein crystal structures has been transformed.

Figure 8.1.8.1| top | pdf | Determination of the protonation states of carboxylic acid side chains in proteins via hydrogen atoms and resolved single and double bond lengths. After Deacon et al. (1997) using CHESS. Reproduced by permission of The Royal Society of Chemistry.