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On optimal placement of molecules in the unit cell.

ABSTRACT: There are currently no rules for a unified, standard way of placing macromolecular structures in the crystal lattice. An analysis of all possible symmetry-equivalent representations of molecular structures in various space groups leads to the concept of the anti-Cheshire symmetry and suggests that the center of a unique structural motif can always be placed within the selected asymmetric unit of the anti-Cheshire cell. The placement of structures according to this suggestion will ensure uniformity of presentation of all structurally equivalent Protein Data Bank models and will therefore diminish the possibility of confusing less crystallographically knowledgeable users of the PDB. The anti-Cheshire cells and their asymmetric units are defined and tabulated for all 65 space groups relevant to macromolecular crystallography that exhibit only rotational symmetry operations.

SUBMITTER: Dauter Z

PROVIDER: S-EPMC4005360 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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On optimal placement of molecules in the unit cell.

Dauter Zbigniew Z

Acta crystallographica. Section D, Biological crystallography 20130419 Pt 5

There are currently no rules for a unified, standard way of placing macromolecular structures in the crystal lattice. An analysis of all possible symmetry-equivalent representations of molecular structures in various space groups leads to the concept of the anti-Cheshire symmetry and suggests that the center of a unique structural motif can always be placed within the selected asymmetric unit of the anti-Cheshire cell. The placement of structures according to this suggestion will ensure uniformi ...[more]

PMID: 23633598

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Project description:Ascertaining the accuracy of the pedicle screw (PS) trajectories is important as PS malpositioning can cause critical complications. We aimed to determine the angle range over which estimation is unreliable; build a low-cost PS placement support system that uses an inertial measurement unit (IMU) to enable the monitoring of surgical tools and PS trajectories, and determine the situations where IMU support would be most beneficial. In PS insertion experiments, we used cadaver samples that included lumbar porcine spines. Computed tomography images obtained before and after PS insertion were viewed. Offsets between the planned and implanted PS trajectories in the freehand and IMU-assisted groups were analyzed. The PS cortical bone breaches were classified according to the Gertzbein and Robbins criteria (GRC). Added head-down tilted sample experiments were repeated wherein we expected a decreased rostro-caudal rotational accuracy of the PS according to the angle estimation ability results. Evaluation of the PS trajectory accuracy revealed no significant advantage of IMU-assisted rostro-caudal rotational accuracy versus freehand accuracy. According to the GRC, IMU assistance significantly increased the rate of clinically acceptable PS positions (RoCA) than the freehand technique. In the head-down tilted sample experiments, IMU assist provided increased accuracies with both rostro-caudal and medial rotational techniques when compared with the freehand technique. In the freehand group, RoCA was significantly decreased in samples with rostral tilting relative to that in the samples without. However, In the IMU-assisted group, no significant difference in RoCA between the samples with and without head-down tilting was observed. Even when the planned PS medial and/or rostro-caudal rotational angle was relatively large and difficult to reproduce manually, IMU-support helped maintain the PS trajectory accuracy and positioning safety. IMU assist in PS placement was more beneficial, especially for larger rostro-caudal and/or medial rotational pedicle angles.

Dataset Information

On optimal placement of molecules in the unit cell.

Publications

On optimal placement of molecules in the unit cell.

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