De novo phasing of two crystal forms of tryparedoxin II using the anomalous scattering from S atoms: a combination of small signal and medium resolution reveals this to be a general tool for solving protein crystal structures
Article first published online: 16 JUN 2004
Acta Crystallographica Section D
Volume 58, Issue 1, pages 21–28, January 2002
How to Cite
Micossi, E., Hunter, W. N. and Leonard, G. A. (2002), De novo phasing of two crystal forms of tryparedoxin II using the anomalous scattering from S atoms: a combination of small signal and medium resolution reveals this to be a general tool for solving protein crystal structures. Acta Crystallographica Section D, 58: 21–28. doi: 10.1107/S0907444901016808
- Issue published online: 16 JUN 2004
- Article first published online: 16 JUN 2004
- Received 20 July 2001, accepted 9 October 2001
- tryparedoxin II;
- anomalous scattering.
The de novo phasing of the structures of two crystal forms of tryparedoxin II from Crithidia fasciculata has been carried out using single-wavelength anomalous diffraction techniques exploiting only the small anomalous signal from the S atoms intrinsic to the native protein. Data were collected at 1.77 Å wavelength, where the Bijvoet ratio is approximately 1.2%. Data collected to dmin = 2.5 Å from a crystal of form I, which has a diffraction limit of dmin = 1.5 Å and a solvent content of ∼46%, produced readily interpretable electron-density maps. When these phases were extended to the resolution limit of the crystals, almost the entire model could be traced automatically. Crystals of form II have a much higher solvent content, ∼72%, and a much lower diffraction limit than form I and at 1.77 Å wavelength yielded data only to dmin = 2.7 Å. Despite the medium resolution of the data for this crystal form, it was possible both to determine the heavy-atom partial structure and then use it to produce, still at dmin = 2.7 Å, an excellent quality interpretable electron-density map. This was then improved by phase extension to the dmin = 2.35 Å diffraction limits of a different crystal for which data were collected on a more intense beamline. The success of this latter structure solution markedly increases the potential use in macromolecular crystal structure determination of the anomalous signal available from S atoms that occur naturally in proteins and, as is discussed, has significant implications for structure determination in the high-throughput era.