ISSN:
1399-0047
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Using Harker's [Harker (1953). Acta Cryst. 6, 731–736] idea of spherically averaged polyatomic groups or `globs' as the units of structure suitable for analyzing low-resolution diffraction data from protein crystals, `globbic' scattering factors have been calculated for main-chain peptide units and amino-acid side-chain groups to 3 Å resolution via Debye's [Debye (1915). Ann. Phys. (Leipzig), 46, 809–823] scattering formula. It is shown that the scattering factors are insensitive to intra-globbic conformational variation and can be approximated fairly well by a single-Gaussian formula, i.e. fg(s) = Zg exp(−1.7Zgs2), where s = (sinθ)/λ and Zg is the total electron count for the atoms of the glob. Phase errors due to the globbic approximation and their effect on electron-density maps at 3.5 Å resolution have been assessed via calculations for the crambin structure; this analysis indicates that the globbic scattering factors will be useful in efforts to develop procedures for direct-methods phasing of diffraction data to ∼3.5 Å resolution from protein crystals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0907444998008208
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