Qiu Weihong, Zhang Luyuan, Kao Ya-Ting, Lu Wenyun, Li Tanping, Kim Jongjoo, Sollenberger Gregory M, Wang Lijuan, Zhong Dongping
Departmens of Physics, OSU Biophysics, Chemical Physics, and Biochemistry Programs, 191 West Woodruff Avenue, The Ohio State University, Columbus, Ohio 43210, USA.
J Phys Chem B. 2005 Sep 8;109(35):16901-10. doi: 10.1021/jp0511754.
Melittin, an amphipathic peptide from honeybee venom, consists of 26 amino acid residues and adopts different conformations from a random coil, to an alpha-helix, and to a self-assembled tetramer under certain aqueous environments. We report here our systematic studies of the hydration dynamics in these conformations using single intrinsic tryptophan (W19) as a molecular probe. With femtosecond resolution, we observed the solvation dynamics occurring in 0.62 and 14.7 ps in a random-coiled primary structure. The former represents bulklike water motion, and the latter reflects surface-type hydration dynamics of proteins. As a comparison, a model tripeptide (KWK) was also studied. At a membrane-water interface, melittin folds into a secondary alpha-helical structure, and the interfacial water motion was found to take as long as 114 ps, indicating a well-ordered water structure along the membrane surface. In high-salt aqueous solution, the dielectric screening and ionic solvation promote the hydrophobic core collapse in melittin aggregation and facilitate the tetramer formation. This self-assembled tertiary structure is also stabilized by the strong hydrophilic interactions of charged C-terminal residues and associated ions with water molecules in the two assembled regions. The hydration dynamics was observed to occur in 87 ps, significantly slower than typical water relaxation at protein surfaces but similar to water motion at membrane interfaces. Thus, the observed time scale of approximately 100 ps probably implies appropriate water mobility for mediating the formation of high-order structures of melittin in an alpha-helix and a self-assembled tetramer. These results elucidate the critical role of hydration dynamics in peptide conformational transitions and protein structural stability and integrity.
蜂毒明肽是一种来自蜜蜂毒液的两亲性肽，由26个氨基酸残基组成，在特定的水环境下会呈现从无规卷曲到α-螺旋，再到自组装四聚体的不同构象。我们在此报告，利用单个内在色氨酸（W19）作为分子探针，对这些构象中的水合动力学进行的系统研究。以飞秒分辨率，我们观察到在无规卷曲的一级结构中，溶剂化动力学分别在0.62皮秒和14.7皮秒发生。前者代表类似 bulk 的水运动，后者反映蛋白质的表面型水合动力学。作为比较，还研究了一种模型三肽（KWK）。在膜 - 水界面，蜂毒明肽折叠成二级α-螺旋结构，发现界面水运动长达114皮秒，表明沿膜表面存在有序的水结构。在高盐水溶液中，介电屏蔽和离子溶剂化促进蜂毒明肽聚集中疏水核心的坍塌，并促进四聚体的形成。这种自组装的三级结构还通过带电荷的C末端残基以及相关离子与两个组装区域中的水分子之间强烈的亲水相互作用而得以稳定。观察到水合动力学在87皮秒发生，明显慢于蛋白质表面典型的水弛豫，但与膜界面的水运动相似。因此，观察到的约100皮秒的时间尺度可能意味着存在适当的水流动性，以介导蜂毒明肽在α-螺旋和自组装四聚体中形成高阶结构。这些结果阐明了水合动力学在肽构象转变以及蛋白质结构稳定性和完整性中的关键作用。
