The estimation of three-phase invariants when anomalous scatterers are present: the limits

Giacovazzo, Carmelo; Ladisa, Massimo; Siliqi, Dritan

doi:10.1107/s0108767303021329

Cited by 2 publications

(1 citation statement)

References 12 publications

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“…Protein crystal structure solution via the tangent formula, using the triplet invariants estimates given six diffraction magnitudes (Hauptman, 1982b;Giacovazzo, 1983), has been definitively abandoned. Indeed, in spite of the efforts expended on it, the success of this approach has been very modest (Giacovazzo et al 2003), even if the reasons for the failures were not well understood. In IL MILIONE the two-step technique (Pä lher et al, 1990;Terwilliger, 1994;Sheldrick, 1998) is exploited (up to four wavelengths may be used); first the structural parameters of the anomalous scatterers are determined, and then the protein phases are assigned and refined.…”

Section: The Sad-mad Casementioning

confidence: 99%

IL MILIONE: a suite of computer programs for crystal structure solution of proteins

et al. 2007

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IL MILIONE is a suite of computer programs devoted to protein crystal structure determination by X‐ray crystallography. It may be used in the following key activities. (a) Ab initio phasing, via Patterson or direct methods. The program may succeed even with structures with up to 6000 non‐H atoms in the asymmetric unit, provided that atomic resolution is available, and with data at quasi‐atomic resolution (1.4–1.5 Å). (b) Single or multiple isomorphous replacement, single‐ or multiple‐wavelength anomalous diffraction, and single or multiple isomorphous replacement with anomalous scattering techniques. In the first step the program finds the heavy‐atom/anomalous scatterer substructure, then automatically uses the above information to phase protein reflections. Phase extension and refinement are performed by electron density modification techniques. (c) Molecular replacement. The orientation and the location of the protein molecules are found via reciprocal space methods. Phase extension and refinement are performed by electron density modification techniques. All the programs integrated into IL MILIONE are controlled by means of a user‐friendly graphical user interface, which is used to input data and to monitor intermediate and final results by means of real‐time updated messages, diagrams and histograms.

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Section: The Sad-mad Casementioning

confidence: 99%

IL MILIONE: a suite of computer programs for crystal structure solution of proteins

et al. 2007

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Locating heavy atoms by integrating direct methods and SIR techniques

Giacovazzo¹,

Moustiakimov²,

Siliqi³

et al. 2004

Acta Cryst Sect A

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Direct methods have been applied to the SIR (single isomorphous replacement) case to estimate structure-factor moduli from diffraction magnitudes. The joint probability distribution function P(E(H),E(p),E(d)) has been calculated by explicitly considering, as an additional primitive random variable, the cumulative error arising from measurements and from lack of isomorphism. The specific feature of the approach is that it provides estimated values of |E(H)| which depend on the experimental diffraction data as well as on errors. Some test structures have been used to check the efficiency of the new estimates. Patterson techniques, using the estimated |E(H)|(2) values as coefficients, as well as a tangent procedure, have been implemented into a computer program to locate the heavy atoms automatically. All the experimental tests show that the new approach provides results highly competitive with the traditional |E(H)|(2) estimates.

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The estimation of three-phase invariants when anomalous scatterers are present: the limits

Cited by 2 publications

References 12 publications

IL MILIONE: a suite of computer programs for crystal structure solution of proteins

IL MILIONE: a suite of computer programs for crystal structure solution of proteins

Locating heavy atoms by integrating direct methods and SIR techniques

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