2aai: Difference between revisions

The plant cytotoxin ricin consists of two disulfide-linked chains, each of about 30,000 daltons. An initial model based on a 2.8 A MIR electron density map has been refined against 2.5 A data using rounds of hand rebuilding coupled with either a restrained least squares algorithm or molecular dynamics (XPLOR). The last model (9) has an R factor of 21.6% and RMS deviations from standard bond lengths and angles of 0.021 A and 4.67 degrees, respectively. Refinement required several peptide segments in the original model to be adjusted translationally along the electron density. A wide range of lesser changes were also made. The RMS deviation of backbone atoms between the original and model 9 was 1.89 A. Molecular dynamics proved to be a very powerful refinement tool. However, tests showed that it could not replace human intervention in making adjustments such as local translations of the peptide chain. The R factor is not a completely satisfactory indicator of refinement progress; difference Fouriers, when observed carefully, may be a better monitor.

[[Category: Collins, E J.]]

[[Category: Ernst, S R.]]

[[Category: Katzin, B J.]]

[[Category: Monzingo, A F.]]

[[Category: Ready, M P.]]

[[Category: Robertus, J D.]]

[[Category: Villafranca, J E.]]

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