Tables for
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

International Tables for Crystallography (2006). Vol. F, ch. 25.2, p. 720   | 1 | 2 |

Section J. P. Abrahams' likelihood-weighted noncrystallographic symmetry restraints

D. E. Tronrudm* and L. F. Ten Eycky J. P. Abrahams' likelihood-weighted noncrystallographic symmetry restraints

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Abrahams (1996)[link] conceived the idea that because some amino-acid side chains can be expected to violate the noncrystallographic symmetry (NCS) of the crystal more than others, one could develop a library of the relative strength with which each atom of each residue type would be held by the NCS restraint. He chose to determine these strengths from the average of the current agreement to the NCS of all residues of the same type. For example, if the lysine side chains do not agree well with their NCS mates, the NCS will be loosely enforced for those side chains. On the other hand, if almost all the valine side chains agree well with their mates, then the NCS will be strongly enforced for the few that do not agree well.

He chose to implement this idea by modifying the source code for the TNT program NCS. Since the calculations involved in implementing this idea are simple, the extent of the modifications were not large.


Abrahams, J. P. (1996). Likelihood-weighted real space restraints for refinement at low resolution. In Proceedings of the CCP4 study weekend. Macromolecular refinement, edited by E. Dodson, M. Moore, A. Ralph & S. Bailey. Warrington: Daresbury Laboratory.Google Scholar

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