摘要:

The method of time‐averaging crystallographic refinement is assessed using a small molecule, α‐cyclodextrin, as a test system. A total of 16 refinements are performed on simulated data. Three resolution ranges of the data are used, the memory relaxation time of the averaging is varied, and several overall temperature factors are used. The most critical factor in the reliable application of time‐averaging is the resolution of the data. The ratio of data to molecular degrees of freedom should be large enough to avoid overfitting of the data by the time‐averaging procedure. The use of a freeR‐factor can aid in determining whether time‐averaging can be reliably applied. Good ensembles of structures are obtained using data up to 1.0 or 2.0 Å resolution. Comparison of electron‐density maps from time‐averaging refinement and anisotropic temperature‐factor refinement indicates that the former technique yields a better representation of the exact

ISSN:1399-0047    

DOI:10.1107/S0907444994007158

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The hydrogen‐bond acceptor functions are analyzed for 672 water molecules in crystal structures of hydrated small biological molecules. Of the 672 water molecules, 26 neither accept hydrogen bonds from O—H or N—H donors, nor coordinate to metal ions. As compensation, they satisfy their acceptor potential with up to four C—H⋯O hydrogen bonds. They are found in hydrated amino acids, purines and pyrimidines, and alkaloids, but not in carbohydrates, nucleosides, nucleotides and steroids. As for conventional hydrogen bonds, the preferred coordination geometry is tetrahedral. No example of a true non‐accepting water molecule is found. A particularly strong C—H hydrogen‐bond donor occurring in many biological molecules is C—H neighbou

ISSN:1399-0047    

DOI:10.1107/S0907444994007614

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Lysozyme structures at six different temperatures in the range 95–295 K have been determined using X‐ray crystallography at a resolution of 1.7 Å. The crystals at lower temperatures had a 7.4% decrease in the unit‐cell volume. The volume change was discontinuous with the volume being near 238 000 Å3from 295 to 250 K and about 220 200 Å3below 180 K. The thermal expansion of the protein has been analyzed and shows anisotropy, which is correlated with local atomic packing and secondary‐structure elements. The lysozyme structure at low temperature is nearly the same as that at high temperature, with only small relative translations and rotations of structure elements including a hinge‐bending rearrangement of two domains. Because of a considerable increase of lattice disorder at low temperature dynamical analysis of internal motion is difficult. The analysis of structural and dynamical properties of well ordered protein‐bo

ISSN:1399-0047    

DOI:10.1107/S0907444994009261

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

A weighted correlation function as a method for computing electron‐density maps is proposed to reduce the errors of the Fourier syntheses performed on inaccurate and/or incomplete data. The formulae are revised for the difference Patterson vector search, for multiple isomorphous replacement (MIR) and single isomorphous replacement (SIR) syntheses and for the difference Fourier synthesis. The examples show that the correlation‐function approach has the potential to provide more reliable results than those obtained by conventional Fourier synthe

ISSN:1399-0047    

DOI:10.1107/S0907444994007195

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The human Clara cell 16 kDa protein (CC10), isolated from lung lavage fluid, has been crystallized in two crystal forms. The first is in space groupP1 and has cell parametersa= 43.04,b= 45.90,c= 51.29 Å and α = 62.46, β = 69.74, γ = 69.43°. Two molecules are present in the unit cell. The second form is in space groupP222, with cell parametersa= 42.24,b= 84.06,c= 40.05 Å and α = β = γ = 90°, and four molecules per unit cell. Its diffraction pattern displays pseudo‐body‐centered symmetry. Both crystal forms diffract

ISSN:1399-0047    

DOI:10.1107/S0907444994009273

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

A non‐glycosylated form of horseradish peroxidasecextracted fromEscherichia coliinclusion bodies and refolded in the presence of haem and Ca2+ions has been used to grow protein crystals suitable for X‐ray diffraction analysis. The crystals are prisms in the trigonal space groupP3112 orP3212 witha=b= 158.9 andc= 114.3 Å, and diffract to 1.9 Å. There are four molecules, each of 34 kDa, in the asymmetric unit. The molecules of the asymmetric unit are related by approximate translational symmetry, resulting in pseudo‐centerings. Data to approximately 15 Å can thus be described by a lattice ofa′ =b′ = 91.7 Å andc′ = 57.1 Å, α = β = 90° and γ

ISSN:1399-0047    

DOI:10.1107/S0907444994008723

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

An Fab fragment from a monoclonal antibody (ME36.1) to the melanoma‐associated GD2 ganglioside has been purified and crystallized in space groupP21with unit‐cell dimensionsa= 37.6,b= 94.1,c= 67.4 Å, β = 101.0°. The crystals, which grow to a size of up to 0.6 × 0.5 × 0.3 mm, diffract to 2.5 Å and native data have been collected to 2.8 Å resolution. The crystal density is 1.22 g ml−1indicating one molecule of 48 kDa per asymmetric unit and a solvent content of 51%. A soluble form of the carbohydrate was obtained from the scarce GD2 glycolipid by enzymatic digestion with ceramide‐glycanase. Small co‐crystals of the Fab–GD2 complex have been obtained. As ME36.1 has been used in immunotherapy to treat malignant melanoma, knowledge of its interactions with the ganglioside could increase

ISSN:1399-0047    

DOI:10.1107/S0907444994007456

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY