Isomorphous substitution and formulas for phase determination

Karle, J.

doi:10.1107/s0365110x66002718

Cited by 199 publications

(218 citation statements)

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“…Fan proposed in 1965 32 the use of direct methods in breaking the phase ambiguity intrinsic to single anomalous diffraction (SAD) and single isomorphous replacement (SIR) methods. Similar investigations were reported by different authors during 1960s and 1970s 33–38. From the early 1980s to the early 2000s, the combination of direct methods with SAD/SIR data was emphasized in direct‐method research worldwide 39–63.…”

Section: Direct Methods In Macromolecular Crystallographysupporting

confidence: 78%

Direct methods beyond small‐molecule crystallography

Fan

2010

Physica Status Solidi (a)

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The development of direct methods outside their traditional field began since the middle 1960s. New applications were explored gradually in four directions. They are the transition of: (i) from single crystals to powder samples, (ii) from X‐ray crystallography to electron microscopy (EM), (iii) from periodic structures to incommensurate structures and (iv) from small molecules to macromolecular structures. The research on methods of solving crystal structures at the Institute of Physics in Beijing has been focused on the last three directions. The transition of direct methods from X‐ray crystallography to EM led to a two‐step image processing technique in high‐resolution electron microscopy (HREM). This technique combines information of EM and that of electron diffraction (ED) revealing the structure of minute crystals that are unsuitable for X‐ray diffraction analysis. The transition of direct methods from periodic crystal structures to incommensurate structures led to the multi‐dimensional direct methods enabling ab initio solution of incommensurate modulated structures and composite structures without relying on an assumed modulation model or even the known basic structure. Finally the combination of direct methods with traditional protein crystallographic methods has greatly enhanced the ability of solving protein structures.

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Section: Direct Methods In Macromolecular Crystallographysupporting

confidence: 78%

Direct methods beyond small‐molecule crystallography

Fan

2010

Physica Status Solidi (a)

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“…When dealing with structures having centrosymmetric heavy-atom arrangements, (17) reduces to either of the two probability formulae given by Karle (1966) according to whether SIR or OAS data are used. On the other hand, while the Karle formulae are not applicable to structures having non-centrosymmetric heavy-atom arrangements, (16) or (17) is very efficient for resolving phase ambiguities in this case.…”

Section: Llmentioning

confidence: 99%

“…This method does not make full use of the information which could be obtained from a single isomorphous pair. Fan (1965a) and Karle (1966) suggested the use of 'component relationships', i.e. the relationships among the real and imaginary components of the structure factors.…”

Section: Introductionmentioning

confidence: 99%

Combining direct methods with isomorphous replacement or anomalous scattering data. I

Fan¹,

Fu-son²,

Qian³

et al. 1984

Acta Cryst Sect A

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A direct-methods procedure has been proposed for separating the phase doublet resulting from the use of either isomorphous replacement or anomalous scattering techniques. The phase doublet is expressed as ~#u= ~h±lA~.l. Formulae combining the structure-factor relationships with the phase-doublet information are given. Problems concerning the practical applications are also discussed. A test calculation with the error-free data for the protein insulin showed a satisfactory result.

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“…If a method can be found to resolve the ambiguity, the OAS method would be a useful technique in protein crystallography, since it is possible to solve a protein structure by either skipping the step of heavy-atomderivative preparation if it contains suitable anomalous scatterers, or using only a heavy-atom derivative which may not be isomorphous to the native protein. Attempts have been made to resolve the phase ambiguity arising from the OAS technique by direct methods since the 1960's (Fan, 1965;Karle, 1966). More recently, Hauptman (1982), Giacovazzo (1983) and Karle (1984) have succeeded in deriving a large number of three-phase structure invariants * Supported in part by the National Natural Science Foundation of China.…”

Section: Introductionmentioning

confidence: 99%

Combining direct methods with isomorphous replacement or anomalous scattering data. VII.Ab initiophasing of one-wavelength anomalous scattering data from a small protein

Hai-Fu¹,

Hao²,

Gu³

et al. 1990

Acta Cryst Sect A

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The previously proposed method [Fan, Han & Qian (1984). Acta Cryst. A40, 495-498;. Acta Cryst. A41, 280-284] has been improved and tested for ab initio phasing of the one-wavelength anomalous scattering data at 2 A, resolution from a known small protein, avian pancreatic polypeptide. Positions of the anomalous scatterers were found by the direct-method program SAPI and used to normalize the anomalous differences before calculating the phase doublets. 2108 independent reflections and about 790 000 Y~2 relationships were involved in the phase derivation. The 'best phases' and the figures of merit obtained from the direct method were used to calculate a Fourier map, which revealed the essential feature of the structure.

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Isomorphous substitution and formulas for phase determination

Cited by 199 publications

References 0 publications

Direct methods beyond small‐molecule crystallography

Direct methods beyond small‐molecule crystallography

Combining direct methods with isomorphous replacement or anomalous scattering data. I

Combining direct methods with isomorphous replacement or anomalous scattering data. VII.Ab initiophasing of one-wavelength anomalous scattering data from a small protein

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