Low-resolution ab initio phasing: problems and advances

If only native amplitudes are used for structure determination, then additional `theoretical' information is necessary to determine their phases. For use in a phasing procedure, this information can be formulated as a selection criterion (figure of merit) which assigns a reliability weight to e...

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Published in:Acta crystallographica. Section D, Biological crystallography. Biological crystallography., 2000-10, Vol.56 (10), p.1223-1232
Main Authors: Lunin, Vladimir Y., Lunina, Natalia L., Petrova, Tatiana E., Skovoroda, Tatiana P., Urzhumtsev, Alexandre G., Podjarny, Alberto D.
Format: Article
Language:English
Subjects:
Chemical Sciences
Cluster Analysis
Computer Simulation
Cristallography
Crystallography
Fourier Analysis
Image Processing, Computer-Assisted
low-resolution ab initio phasing
Models, Molecular
Neutron Activation Analysis
Nucleic Acid Conformation
Protein Conformation
Proteins - chemistry
Ribonucleases - chemistry
Ribosomes - ultrastructure
RNA, Transfer, Asp - chemistry
Thermus thermophilus - ultrastructure
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Summary:If only native amplitudes are used for structure determination, then additional `theoretical' information is necessary to determine their phases. For use in a phasing procedure, this information can be formulated as a selection criterion (figure of merit) which assigns a reliability weight to every trial phase set and distinguishes the closest ones to the true phase set. Different types of additional information may be tested as a selection criterion: electron‐density histograms, connectivity properties, statistical likelihood, atomicity etc. A common feature of such criteria is that they do not unambiguously judge the phase quality at low resolution. Nevertheless, the selection of the phase sets with best criterion values increases the ratio of good phase sets in the ensemble considered. An approximate solution of the phase problem may then be found by averaging the selected phase sets. Cluster analysis of the selected phase sets and averaging within clusters allow further improvement of this solution.
ISSN:1399-0047
0907-4449
1399-0047
DOI:10.1107/S0907444900010088