Electronic Reprint Biological Crystallography Soaking: the Effect of Osmotic Shock on Tetragonal Lysozyme Crystals Biological Crystallography Soaking: the Effect of Osmotic Shock on Tetragonal Lysozyme Crystals
Electronic Reprint Biological Crystallography Soaking: the Effect of Osmotic Shock on Tetragonal Lysozyme Crystals Biological Crystallography Soaking: the Effect of Osmotic Shock on Tetragonal Lysozyme Crystals
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电子转载 生物晶体学浸泡：渗透压冲击对四方溶菌酶晶体的影响 生物晶体学浸泡：渗透压冲击对四方溶菌酶晶体的影响
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Garcõ Âa
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F. J. L. Opez;A. Moraleda;L. Gonzalez;A. Carazo;J. M. García;Lo  Pez;F. J. Lo  Pez;L. A. Gonza Âlez;A. Ârez;J. Carazo;Garcõ Âa
本文的作者可以在他们自己的网站上加载此重印本，前提是保留此封面页。未经 IUCr 事先书面许可，不得转载本文或将其存储在电子数据库等中。当蛋白质晶体浸泡在离子强度与其生长环境完全不同的溶液中时，它们就会破裂。以四方溶菌酶为例，证明高渗和低渗浸泡所涉及的力和导致裂纹形成的机制是不同的。四方溶菌酶晶体对低渗冲击非常敏感，经过一定的等待时间后，总是会出现垂直于晶体 c 轴的特征图案的裂纹。相反，高渗冲击可以更好地承受：裂纹不显示任何确定性模式，仅在离子强度差异较大时才可见，并且在一定时间后会发生晶体重建现象并且裂纹消失。在晶格水平上，晶胞体积在低渗冲击下膨胀，在高渗条件下收缩。然而，晶胞的压缩是各向异性的：c 轴被压缩到最小值，超过该值，尽管晶胞体积继续收缩，但它仍会膨胀。这种行为是晶体所带正电荷以及沿晶体 c 轴存在通道的直接结果。这两个特征都导致了吉布斯±唐南效应，该效应限制了离子的自由交换并影响了通道内水的运动并与蛋白质结合。
Author(s) of this paper may load this reprint on their own web site provided that this cover page is retained. Republication of this article or its storage in electronic databases or the like is not permitted without prior permission in writing from the IUCr. Protein crystals crack when they are soaked in a solution with ionic strength suf®ciently different from the environment in which they grew. It is demonstrated for the case of tetragonal lysozyme that the forces involved and the mechanisms that lead to the formation of cracks are different for hypertonic and hypotonic soaking. Tetragonal lysozyme crystals are very sensitive to hypotonic shocks and, after a certain waiting time, cracks always appear with a characteristic pattern perpendicular to the crystallographic c axis. Conversely, a hypertonic shock is better withstood: cracks do not display any deterministic pattern, are only visible at higher differences in ionic strength and after a certain time a phenomenon of crystal reconstruction occurs and the cracks vanish. At the lattice level, the unit-cell volume expands in hypotonic shock and shrinks under hypertonic conditions. However, the compression of the unit cell is anisotropic: the c axis is compressed to a minimum, beyond which it expands despite the unit-cell volume continuing to shrink. This behaviour is a direct consequence of the positive charge that the crystals bear and the existence of channels along the crystallographic c axis. Both features are responsible for the Gibbs±Donnan effect which limits the free exchange of ions and affects the movement of water inside the channels and bound to the protein.