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Connectivity-based ab initio phasing: from low resolution to a secondary structure.

Natalia Lunina1, Vladimir Y Lunin, Alexandre Urzhumtsev

  • 1Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia.

Acta Crystallographica. Section D, Biological Crystallography
|September 23, 2003
PubMed
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The connectivity-based phasing method enables ab initio phase determination, revealing secondary structures like alpha-helices and beta-strands in small unit cell crystals.

Area of Science:

  • Crystallography
  • Structural Biology
  • Biophysics

Background:

  • Ab initio phasing methods are crucial for determining protein structures.
  • Current methods are limited by resolution, especially for large macromolecules.
  • Small unit cell crystals offer potential for higher resolution phase determination.

Purpose of the Study:

  • To evaluate the effectiveness of connectivity-based phasing for ab initio phase determination.
  • To assess the resolution achievable for identifying secondary structure elements.
  • To demonstrate the method's utility in analyzing small unit cell protein crystals.

Main Methods:

  • Utilized the connectivity-based phasing method for ab initio phase determination.
  • Applied the method to macromolecular crystals with small unit cells.

Related Experiment Videos

  • Analyzed resulting electron density maps for structural features.

    • Main Results:

    • Successfully determined phases for several hundred reflections.
    • Identified secondary structure elements, including alpha-helices and beta-strands, in phased maps.
    • Observed all three alpha-helices in Er-1 and alpha-helices plus beta-strands in Protein G.

    Conclusions:

    • Connectivity-based phasing can yield interpretable maps for small unit cell crystals.
    • The method facilitates the identification of secondary structure elements directly from ab initio phased data.
    • This approach enhances the potential for de novo structure solution in specific crystallographic cases.