| Abstract |
The native-SAD method (single-wavelength anomalous diffraction) offers a convenient route to solving the phase problem in macromolecular X-ray crystallography by exploiting the anomalous scattering of light elements, such as sulfur and phosphorus, naturally present in biological macromolecules. Phasing with native crystals is adventurous because it renders unnecessary the incorporation of heavier elements, which can be problematic both in protein expression and in degradation of crystal diffraction quality. However, the anomalous scattering from sulfur and phosphorus is very weak (<|ΔF±|>/<|F|> ~ 1-2%) in the radiation energy range (5 – 18 keV) typically accessible at macromolecular crystallography beamlines. Therefore, the success of native-SAD phasing depends heavily on the precision and accuracy of diffraction data. Recent developments in data collection strategies and multi-crystal averaging method have increased the successful rate of native-SAD phasing significantly. The effectiveness of these new methods will be illustrated with 30 real-life cases, including large macromolecular complexes (> 200 kDa). The opportunities and challenges in applying native-SAD method in the tender X-ray region (< 5 keV) will be discussed. |
