PROTEIN FLEXIBILITY AND ADAPTABILITY SEEN IN 25 CRYSTAL FORMS OF T4 LYSOZYME
PROTEIN FLEXIBILITY AND ADAPTABILITY SEEN IN 25 CRYSTAL FORMS OF T4 LYSOZYME
复制标题
DOI：
10.1006/jmbi.1995.0396
复制
发表时间：
1995-07-21
影响因子：
5.6
通讯作者：
MATTHEWS, BW
中科院分区：
文献类型：
--
作者：
ZHANG, XJ;WOZNIAK, JA;MATTHEWS, BW
以25种不同晶型的T_4溶菌酶突变体的晶体结构进行了测定。这提供了一个异常多样化的数据库，以比较一组密切相关的蛋白质在不同晶体包装环境中的结构和动力学。一般来说，更紧密包装的晶体比那些高度水合的晶体更好，尽管野生型晶体形式是一个例外。蛋白质形成相对开放但稳定的晶格的能力可能有助于解释为什么许多突变体以这种形式结晶。在不同的晶体环境中，溶菌酶分子以2倍、3倍、4倍和5倍对称以及各种类型的螺旋缔合。“背靠背”二聚体缔合和“头对尾”2（1）螺旋缔合特别常见，每种都有六种以上的晶体形式。4倍和5倍的缔合模式是密切相关的，并提供了一个例子，准等效协会设想的卡斯帕和Klug.In不同的晶体环境中的溶菌酶分子显示的铰链弯曲角之间的氨基和羧基末端域的范围超过50度。铰链弯曲角的大的变化不仅观察到在铰链区突变的溶菌酶，但远离这个网站的突变的分子。这表明铰链弯曲是溶菌酶分子的固有特性，而不是由于突变而造成的人为现象。当铰链弯曲角增加约15度超过野生型中所见时，铰链弯曲区域中5个残基的侧链中存在明显的构象变化。骨架的变化定位在残基13，59和80附近，但不包括在φ psi的显着变化。不同结构的比较表明，晶体接触扰动的蛋白质骨架结构的0.2至0.5埃。这些扰动对于螺旋和β-折叠链具有相同的量级，表明蛋白质结构可以通过氢键（即链-链）或非氢键（即螺旋-螺旋）相互作用同样好地定义和维持。不同晶体学环境中溶菌酶结构之间的差异与其他独立确定的蛋白质晶体结构的比较一致。他们认为，蛋白质结构通常会发生0.2至0.5埃的低能量构象变化。在各个晶体结构中的侧链的热因子与平均值一致（总体相关性0.74），表明晶体中的侧链流动性代表溶液中的侧链流动性。然而，主链原子的热因子不太一致（与平均值的相关性在0.16至0.76之间）。这表明，在极端情况下，某些晶体形式中的主链运动可能受到分子间晶体接触的限制，以至于它不再代表溶液中的动态行为。
The structures of various mutants of T4 lysozyme have been determined in 25 non-isomorphous crystal forms. This provides an unusually diverse data base to compare the structures and dynamics of a closely related set of proteins in different crystal packing environments.In general, the more tightly packed crystals diffract better than those that are highly hydrated although the wild-type crystal form is an exception. The ability of the protein to form a relatively open but stable lattice may help explain why many of the mutants crystallize in this form.In different crystalline environments, the lysozyme molecules associate with 2-fold, 3-fold, 4-fold, and 5-fold symmetry, as well as with various types of screw associations. A ''back-to-back'' dimeric association, and a ''head-to-tail'' 2(1) screw association, are especially common, each occurring in more than half a dozen crystal forms. The 4-fold and 5-fold modes of association are closely related and provide an example of quasi-equivalent association as envisaged by Caspar and Klug.In different crystal environments the lysozyme molecules display a range of over 50 degrees in the hinge-bending angle between the amino and carboxyterminal domains. Large variations in the hinge-bending angle are observed not only for lysozymes with mutations in the hinge region, but for molecules with mutations far from this site. This suggests that hinge-bending is an intrinsic property of the lysozyme molecule and is not an artifact due to mutation. As the hinge-bending angle increases about 15 degrees beyond that seen in wild-type there is a distinct conformations change in the side-chains of five residues in the hinge-bending region. Changes in the backbone are localized near residues 13, 59 and 80, but do not include significant changes in phi psi.Comparison of the different structures indicates that crystal contacts perturb the backbone structure of the protein by 0.2 to 0.5 Angstrom. These perturbations are of the same magnitude for helices and beta-sheet strands, suggesting that protein structures can be defined and maintained equally well by hydrogen-bonding (i.e. strand-strand) or by non-hydrogen-bonding (i.e. helix-helix) interactions. The discrepancies between the lysozyme structures in different crystallographic environments are in line with other comparisons of independently determined protein crystal structures. They suggest that protein structures in general are subject to low energy changes in conformation of 0.2 to 0.5 Angstrom. The thermal factors of the side-chains in the individual crystal structures agree well with the average values (overall correlation 0.74), suggesting that side-chain mobility in the crystals is representative of side-chain mobility in solution. The thermal factors of the main-chain atoms, however, do not agree so well (correlations with the average ranging from 0.16 to 0.76). This suggests that in extreme cases the main-chain motion in some crystal forms may be constrained by intermolecular crystal contacts to such a degree that it is no longer representative of dynamic behavior in solution.