Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Chemistry and Pharmacology
At 3 to 4 Å resolution, the electron density of a protein may be modeled by a continuous chain of `globs' representing the amide region of the peptide backbone and the side-chain residues. Group scattering factors are derived from a trans planar CαC=ONCα backbone segment and most favored side-chain conformer for 18 different amino acids. Trial calculations indicate that the phase error and crystallographic residual comparing the atomic and `globic' models rapidly decrease from high to low resolution. At 3 Å resolution, the phase error is approximately 80°. These results indicate that the electron density of a protein composed of N amino acid residues may be adequately modeled by 2N globs at low resolution.
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