VLD algorithm and hybrid Fourier syntheses

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Abstract

The VLD (vive la difference) phasing algorithm combines the model electrondensity with the difference electron density via reciprocal space relationships toobtain new phase values and drive them to the correct values. The process isiterative and has been applied to small and medium-size structures and toproteins. Hybrid Fourier syntheses show properties that are intermediatebetween those of the observed synthesis (whose peaks should correspond to themost probable atomic positions) and those of the difference synthesis (whosepositive and negative peaks should correspond to missed atomic positions and tofalse atoms of the model, respectively). Thanks to these properties some hybridsyntheses can be used in the phase extension and refinement step, to reduce themodel bias and more rapidly move to the target structure. They have beenrecently revisited via the method of joint probability distribution functions[Burla, Carrozzini, Cascarano, Giacovazzo & Polidori (2011). Acta. Cryst. A67,447-455]. The results suggested that VLD could be usefully combined, for abinitio phasing, with the hybrid rather than with the difference Fourier synthesis.This paper explores the feasibility of such a combination and shows that theoriginal VLD algorithm is only one of several variants, all with relevant phasingcapacity. The study explores the role of several parameters in order to design astandard procedure with optimized phasing power.

Autore Pugliese

Tutti gli autori

  • Burla M.C.; Carrozzini B.; Cascarano G.L.; Giacovazzo C.; Polidori G.

Titolo volume/Rivista

Journal of applied crystallography

Anno di pubblicazione

2012

ISSN

0021-8898

ISBN

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