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  • Title: Structure determination of plastocyanin from a specimen with a hemihedral twinning fraction of one-half.
    Author: Redinbo MR, Yeates TO.
    Journal: Acta Crystallogr D Biol Crystallogr; 1993 Jul 01; 49(Pt 4):375-80. PubMed ID: 15299512.
    Abstract:
    The structure determination of a macromolecule from a hemihedrally twinned crystal specimen with a twinning fraction of one-half is described. Twinning was detected by analysis of crystal-packing density and intensity statistics. The structure was solved using molecular replacement, and the positioned search model was used to overcome the twinning by a novel method of 'detwinning' the observed data. Estimates of the unobservable crystallographic intensities from each of the twin domains were obtained and used to refine the model. The structure of a new algal plastocyanin from Chlamydomonas reinhardtii was determined by this method to 1.6 A resolution with a 'twinned' R factor of 15.6%. Additional data from a crystal specimen with a low twinning fraction were used to establish the accuracy of the structure solution from the perfectly twinned data, and to finalize the refinement to 1.5 A resolution and a true R factor of 16.8%. Methods for detecting twinning and obtaining a molecular-replacement solution in the presence of twinning are discussed.
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