Sanders Lori K, Xian Wujing, Guáqueta Camilo, Strohman Michael J, Vrasich Chuck R, Luijten Erik, Wong Gerard C L
Department of Materials Science and Engineering, The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801-2920, USA.
Proc Natl Acad Sci U S A. 2007 Oct 9;104(41):15994-9. doi: 10.1073/pnas.0705898104. Epub 2007 Oct 2.
The aim for deterministic control of the interactions between macroions in aqueous media has motivated widespread experimental and theoretical work. Although it has been well established that like-charged macromolecules can aggregate under the influence of oppositely charged condensing agents, the specific conditions for the stability of such aggregates can only be determined empirically. We examine these conditions, which involve an interplay of electrostatic and osmotic effects, by using a well defined model system composed of F-actin, an anionic rod-like polyelectrolyte, and lysozyme, a cationic globular protein with a charge that can be genetically modified. The structure and stability of actin-lysozyme complexes for different lysozyme charge mutants and salt concentrations are examined by using synchrotron x-ray scattering and molecular dynamics simulations. We provide evidence that supports a structural transition from columnar arrangements of F-actin held together by arrays of lysozyme at the threefold interstitial sites of the actin sublattice to marginally stable complexes in which lysozyme resides at twofold bridging sites between actin. The reduced stability arises from strongly reduced partitioning of salt between the complex and the surrounding solution. Changes in the stability of actin-lysozyme complexes are of biomedical interest because their formation has been reported to contribute to the persistence of airway infections in cystic fibrosis by sequestering antimicrobials such as lysozyme. We present x-ray microscopy results that argue for the existence of actin-lysozyme complexes in cystic fibrosis sputum and demonstrate that, for a wide range of salt conditions, charge-reduced lysozyme is not sequestered in ordered complexes while retaining its bacterial killing activity.
对水介质中大分子离子间相互作用进行确定性控制的目标，激发了广泛的实验和理论研究工作。尽管已经充分证实，带相同电荷的大分子在带相反电荷的凝聚剂影响下会聚集，但此类聚集体稳定性的具体条件只能通过实验确定。我们通过使用一个定义明确的模型系统来研究这些条件，该系统由F - 肌动蛋白（一种阴离子棒状聚电解质）和溶菌酶（一种阳离子球状蛋白质，其电荷可通过基因改造）组成。利用同步加速器X射线散射和分子动力学模拟，研究了不同溶菌酶电荷突变体和盐浓度下肌动蛋白 - 溶菌酶复合物的结构和稳定性。我们提供的证据支持了一种结构转变，即从溶菌酶阵列在肌动蛋白亚晶格的三重间隙位点将F - 肌动蛋白维系在一起的柱状排列，转变为溶菌酶位于肌动蛋白之间的双重桥接位点的边缘稳定复合物。稳定性降低源于复合物与周围溶液之间盐的分配大幅减少。肌动蛋白 - 溶菌酶复合物稳定性的变化具有生物医学意义，因为据报道它们的形成通过隔离溶菌酶等抗菌物质，导致囊性纤维化患者气道感染持续存在。我们展示的X射线显微镜结果表明囊性纤维化痰液中存在肌动蛋白 - 溶菌酶复合物，并证明在广泛的盐条件下，电荷减少的溶菌酶在保留其细菌杀伤活性的同时，不会被隔离在有序复合物中。
