Method for modelling the electron density of a crystal
First Claim
1. A diffractometer system for generating an image of the electron density distribution of a macromolecule crystal, the system comprising:
- (a) a source of radiation that diffracts when directed onto the macromolecule crystal;
(b) a detector for collecting an intensity versus position diffraction pattern of the macromolecule crystal;
(c) a processor for converting the diffraction pattern of the crystal into the electron density distribution of the macromolecule crystal, the processor including;
(i) means for determining the asymmetric unit of the crystal;
(ii) means for distributing a number of scattering bodies within the asymmetric unit;
(iii) means for repeatedly generating a scattering amplitude pattern of the scattering bodies, correlating that pattern against the diffraction pattern of the crystal, and moving the scattering bodies a fixed distance to increase the correlation between the patterns of the crystal and the scatterers;
(iv) means for reducing the size of the fixed distance in iii; and
(v) means for ending step iii after the size of the fixed distance reaches a predetermined value, and(d) a graphical display device for generating an image of the three-dimensional electron density distribution of the crystal, wherein the arrangement of scattering bodies in the ending distribution represents the electron density distribution of the macromolecule crystal.
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Abstract
A method for modelling the electron density distribution of a macromolecule in a defined asymmetric unit of a crystal lattice having locations of uniformly diffracting electron density includes the steps of: producing an initial distribution of scattering bodies within a asymmetric unit having the same dimensions as the defined asymmetric unit; calculating scattering amplitudes of the initial distribution and determining the correlation between the calculated scattering amplitudes and the normalized amplitudes; moving at least one of the scattering bodies within the asymmetric unit to create a modified distribution; calculating scattering amplitudes and phases of the modified distribution and determining the correlation between the calculated amplitudes and the normalized values; and producing a final distribution of scattering bodies by repeating moving and calculating steps until the correlation between the calculated scattering amplitudes and the normalized amplitudes is effectively maximized, the final distribution of scattering bodies defining the electron density of the crystal.
36 Citations
24 Claims
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1. A diffractometer system for generating an image of the electron density distribution of a macromolecule crystal, the system comprising:
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(a) a source of radiation that diffracts when directed onto the macromolecule crystal; (b) a detector for collecting an intensity versus position diffraction pattern of the macromolecule crystal; (c) a processor for converting the diffraction pattern of the crystal into the electron density distribution of the macromolecule crystal, the processor including; (i) means for determining the asymmetric unit of the crystal; (ii) means for distributing a number of scattering bodies within the asymmetric unit; (iii) means for repeatedly generating a scattering amplitude pattern of the scattering bodies, correlating that pattern against the diffraction pattern of the crystal, and moving the scattering bodies a fixed distance to increase the correlation between the patterns of the crystal and the scatterers; (iv) means for reducing the size of the fixed distance in iii; and (v) means for ending step iii after the size of the fixed distance reaches a predetermined value, and (d) a graphical display device for generating an image of the three-dimensional electron density distribution of the crystal, wherein the arrangement of scattering bodies in the ending distribution represents the electron density distribution of the macromolecule crystal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for generating an image of the electron density distribution of a macromolecule crystal in a defined asymmetric unit of a crystal lattice, the system comprising
(a) means for converting a diffraction pattern of the macromolecule crystal into computer usable data, the diffraction pattern obtained with a diffractometer; -
(b) means for determining the asymmetric unit of the crystal from the computer usable data; (c) means for distributing a number of scattering bodies within the asymmetric unit; (d) means for repeatedly generating a scattering amplitude pattern of the scattering bodies, correlating that pattern against the diffraction pattern of the crystal, and moving the scattering bodies a fixed distance to increase the correlation between the patterns of the crystal and the scatterers; (e) means for reducing the size of the fixed distance in c; and (f) means for ending step c after the fixed distance reaches a predetermined value; and (g) means for graphically displaying images of the electron density distribution of the macromolecule crystal. - View Dependent Claims (10, 11)
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12. A method of generating an image of a macromolecule crystal, the method including the following steps:
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(a) converting diffraction data of the macromolecule crystal into computer usable normalized amplitudes, the data being produced with a diffractometer; (b) determining the dimensions of an asymmetric unit of the crystal; (c) producing an initial distribution of scattering bodies within an asymmetric unit having the same dimensions as the asymmetric unit determined in step (b); (d) calculating scattering amplitudes of the initial distribution and determining the correlation between the calculated scattering amplitudes and the computer usable normalized amplitudes from the diffraction data; (e) moving at least one of said scattering bodies within the asymmetric unit a predefined distance to create a modified distribution; (f) calculating scattering amplitudes of said modified distribution and determining the correlation between said calculated amplitudes and the normalized amplitudes; (g) producing a final distribution of scattering bodies by repeating steps (e) and (f), and during at least one step, reducing the predefined distance in step (e), until the correlation between said calculated scattering amplitudes and the normalized amplitudes is effectively maximized, said final distribution of scattering bodies representing the electron density of the crystal; and (h) graphically displaying an image of the final distribution of scattering bodies. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of generating an image of a macromolecule crystal from diffraction data for the macromolecule, the method including the following steps:
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(a) receiving the diffraction data from a diffractometer; (b) determining the dimensions of an asymmetric unit of the crystal from the diffraction data; (c) converting a portion of the diffraction data for the macromolecule into normalized amplitudes; (d) randomly distributing a plurality of scattering bodies in a representation of the asymmetric unit of the macromolecule crystal, the number of bodies in the asymmetric unit being less than the number of non-hydrogen atoms in the macromolecule crystal; (e) moving the plurality of scattering bodies by predetermined distances into a final distribution, whereby the fit between the scattering amplitudes of the final distribution and the amplitudes of the diffraction pattern of the crystal is effectively maximized, the final distribution representing an image of the macromolecule crystal; (f) displaying a representation of the final distribution of scattering bodies. - View Dependent Claims (22, 23, 24)
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Specification