Biomedical subjects
Publications and source records attributed to G Tsoucaris.
A new development of the TWIN algorithm is described and used for phase extension/refinement in supramolecular complexes. A small number of phased reflections at low resolution are sufficient for the quasi-automated determination of all atomic coordinates, including disordered atoms.
Phase extension from lower to higher resolution by using an upgraded TWIN variables algorithm [Hountas & Tsoucaris (1995). Acta Cryst. A51, 754-763] in protein molecules with close to 1,000 non-H atoms is presented. Three points of this procedure are of particular interest. (i) The use of a set of auxiliary variables providing a satisfactory fit for many kinds of constraints: the new algorithm works efficiently despite the extreme 'dilution' of very limited initial phase information into a much larger set of auxiliary variables. (ii) The extension of this auxiliary variables set beyond the resolution of the observed data, which enhances the phase extension in a so-called 'super-resolution' sphere. (iii) The use of the crystallographic symmetry as a new figure of merit and as a reliable test for the correctness of the phase-extension process allows an efficient screening.
The complex beta-cyclodextrin-1,7-dioxaspiro[5,5]undecane nonahydrate, C42H70O35.C9H16O2.9H2O, belongs to the class of beta-cyclodextrin dimeric-type complexes. The racemic guest molecule is present in a disordered position. Both enantiomers are located in two different regions inside the channel formed by the host dimers.
The crystal of the 1:1 complex of 3,3-dimethylbutylamine with cyclomaltoheptaose (beta CD, beta-cyclodextrin) is monoclinic C2 with a = 19.187(9), b = 24.56(1), c = 15.893(7) A, beta = 108.77(4) degrees, V = 7091 A3, and Z = 4. Two beta CD molecules, held together by intermolecular hydrogen bonds involving HO-3, form dimers, in the cavities of which two 3,3-dimethylbutylamine and two water molecules are accommodated. The guest molecule is completely enclosed in the cavity. The amino group is located at the secondary-hydroxyl-group side, and is hydrogen-bonded to the entrapped water molecules. The dimers form channels along the c axis. The inter-dimer space is filled with 10.7 water molecules that are distributed over 14 sites, and there is a dense network of hydrogen bonds involving the water molecules and the beta CD hydroxyl groups.
Various types of human stratum corneum (sheets or callus) were exposed, in parallel and perpendicular geometry, to the high flux of X rays produced by a synchrotron radiation source. Under these conditions, very clear and rich diffraction patterns, corresponding to the supramolecular organization of stratum corneum proteins and lipids, were obtained. The comparative study of normal or delipidized stratum corneum sheets and membrane couplets allows one to attribute certain diffraction features to lipids. Our results in the 3-7-nm range show two different distances for lipid bilayers. Concerning the protein nature of normal stratum corneum, the results show that keratin would occur in the beta form, whereas for callus it is in the alpha form. Indeed, normal stratum corneum sheets never display the 0.514-nm characteristic of alpha keratin. This result means that the supramolecular organization of keratin could depend on the keratinization process. Finally, our studies also confirm the presence of a still-unknown protein component existing in the beta form that would be located either inside the corneocytes or in some dilatated zones of the intercellular spaces.
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