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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1023-1035 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Previous atomic force microscopy (AFM) studies and periodic bond-chain (PBC) analyses of tetragonal lysozyme crystals have suggested that the (110) face consists of chains of molecules related to one another by 43 axes parallel to the crystal face. In this study, high-resolution AFM images of the (110) face were obtained and analyzed in order to verify this prediction. A computer program was employed which constructs the theoretical AFM image corresponding to a specific crystallographic molecular-packing arrangement and AFM tip shape. The packing arrangement and tip shape were varied in order to obtain the maximum possible correlation between experimental and theoretical images. The prediction from PBC analysis of an arrangement involving 43 helices was confirmed in this manner, while the alternate arrangement, consisting of molecules related to one another by 21 axes, was not observed. However, the surface structure was found to differ significantly even from this crystallographic arrangement. The molecules were found to pack slightly closer about what will become the 43 axes within the interior of the crystal, suggesting the occurrence of surface reconstruction or rearrangement on the tetragonal lysozyme (110) face. This study represents a new approach for more precise determination of the molecular-packing arrangements on protein crystal faces employing AFM.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1604-1605 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Crystals of the restriction endonuclease EcoRII have been obtained by the vapor-diffusion technique in the presence of ammonium sulfate or polyethylene glycol. The best crystals were grown with ammonium sulfate as a precipitant. Crystals with dimensions of up to 0.6 × 0.6 × 0.6 mm have been observed. The crystals diffract to about 4.0 Å resolution at a cryo-temperature of 100 K using a rotating-anode X-ray source and a Rigaku R-AXIS IV imaging-plate detector. The space group has been determined to be either I23 or I213, with unit-cell parameters a = b = c = 160.3 Å, α = β = γ = 90°. The crystal asymmetric unit contains two protein molecules, and self-rotation function analysis shows a pseudo-twofold symmetry relating the two monomers. Attempts to improve the resolution of crystal diffraction and to search for heavy-atom derivatives are under way.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 899-904 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Anions have been shown to play a dominant role in the crystallization of chicken egg-white lysozyme from salt solutions. Previous studies employing X-ray crystallography have found one chloride ion binding site in the tetragonal crystal form of the protein and four nitrate ion binding sites in the monoclinic form. In this study the anion positions in the tetragonal form were determined from the difference Fourier map obtained from lysozyme crystals grown in bromide and chloride solutions. Five possible anion-binding sites were found in this manner. Some of these sites were in pockets containing basic residues while others were near neutral, but polar, residues. The sole chloride ion binding site found in previous studies was confirmed, while four further sites were found which corresponded to the four binding sites found for nitrate ions in monoclinic crystals. The study suggests that most of the anion-binding sites in lysozyme remain unchanged even when different anions and different crystal forms of lysozyme are employed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1012-1022 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Measurements of the macroscopic growth rates of the (101) face of tetragonal lysozyme crystals indicate an unusual dependence on the supersaturation [Forsythe et al. (1999), Acta Cryst. D55, 1005–1011] similar to that observed for the (110) face. As performed previously for the (110) face, the surface packing arrangement for the (101) face was constructed in this study based on earlier microscopic observations and theoretical analysis of the internal molecular packing. This allowed the minimum growth unit for this face to be identified as a tetramer corresponding to a single turn of helices centered about the 43 axes and the minimum growth step to be identified as of unimolecular height. A macroscopic mathematical model for the growth of the (101) face was developed based on the reversible formation of multimeric growth units in solution and the addition of a unit to the crystal face by dislocation and two-dimensional nucleation mechanisms. The calculations showed that the best fits were obtained for tetramer or octamer growth units in this model. This and other evidence suggests that while growth may proceed by a variety of growth units, the average size of these units is between that of a tetramer and an octamer.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1036-1045 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A high-resolution atomic force microscopy (AFM) study has shown that the molecular packing on the tetragonal lysozyme (110) face corresponds to only one of two possible packing arrangements, suggesting that growth layers on this face are of bimolecular height [Li et al. (1999). Acta Cryst. D55, 1023–1035]. Theoretical analyses of the packing also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size, corresponding to the 43 helices in the crystal. In this study, an AFM linescan technique was used to measure the dimensions of individual growth units on protein crystal faces as they were being incorporated into the lattice. Images of individual growth events on the (110) face of tetragonal lysozyme crystals were observed, shown by jump discontinuities in the growth step in the linescan images. The growth-unit dimension in the scanned direction was obtained from these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme growth-unit sizes were obtained. A variety of unit sizes corresponding to 43 helices were shown to participate in the growth process, with the 43 tetramer being the minimum observed size. This technique represents a new application for AFM, allowing time-resolved studies of molecular processes to be carried out.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1005-1011 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Previous extensive measurements of the growth rates of the (110) face of tetragonal lysozyme crystals have shown unexpected dependencies on the supersaturation. In this study, similar growth-rate measurements were performed for the (101) faces of the crystals. The data show a similar dependence on the supersaturation, becoming appreciable only at high supersaturations, reaching a maximum value and then decreasing. The (101) growth rates are larger at low supersaturations than the (110) growth rates under the same conditions and are smaller at high supersaturations. These trends suggest that the growth mechanism of the (101) face is similar to that of the (110) face: both processes involve the addition of multimeric growth units formed in solution, but the average size of the units for the (101) face is likely to be smaller than for the (110) face.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 776-785 
    ISSN: 0006-3592
    Keywords: protein crystallization ; impurities ; lysozyme ; purification ; solubility ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: While bulk crystallization from impure solutions is used industrially as a purification step for a wide variety of materials, it is a technique that has rarely been used for proteins. Proteins have a reputation for being difficult to crystallize and high purity of the initial crystallization solution is considered paramount for success in the crystallization. Although little is written on the purifying capability of protein crystallization or of the effect of impurities on the various aspects of the crystallization process, recent published reports show that crystallization shows promise and feasibility as a purification technique for proteins.To further examine the issue of purity in macromolecule crystallization, this study investigates the effect of the protein impurities, avidin, ovalbumin, and conalbumin at concentrations up to 50%, on the solubility, crystal face growth rates, and crystal purity of the protein lysozyme. Solubility was measured in batch experiments while a computer controlled video microscope system was used to measure the {110} and {101} lysozyme crystal face growth rates. While little effect was observed on solubility and high crystal purity was obtained ( 〉 99.99%), the effect of the impurities on the face growth rates varied from no effect to a significant face specific effect leading to growth cessation, a phenomenon that is frequently observed in protein crystal growth. The results shed interesting light on the effect of protein impurities on protein crystal growth and strengthen the feasibility of using crystallization as a unit operation for protein purification. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:776-785, 1998.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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