Makabe Koki, Biancalana Matthew, Yan Shude, Tereshko Valentina, Gawlak Grzegorz, Miller-Auer Hélène, Meredith Stephen C, Koide Shohei
Department of Biochemistry and Molecular Biology, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA.
J Mol Biol. 2008 Apr 25;378(2):459-67. doi: 10.1016/j.jmb.2008.02.051. Epub 2008 Mar 4.
beta-Rich self-assembly is a major structural class of polypeptides, but still little is known about its atomic structures and biophysical properties. Major impediments for structural and biophysical studies of peptide self-assemblies include their insolubility and heterogeneous composition. We have developed a model system, termed peptide self-assembly mimic (PSAM), based on the single-layer beta-sheet of Borrelia outer surface protein A. PSAM allows for the capture of a defined number of self-assembly-like peptide repeats within a water-soluble protein, making structural and energetic studies possible. In this work, we extend our PSAM approach to a highly hydrophobic peptide sequence. We show that a penta-Ile peptide (Ile(5)), which is insoluble and forms beta-rich self-assemblies in aqueous solution, can be captured within the PSAM scaffold in a form capable of self-assembly. The 1.1-A crystal structure revealed that the Ile(5) stretch forms a highly regular beta-strand within this flat beta-sheet. Self-assembly models built with multiple copies of the crystal structure of the Ile(5) peptide segment showed no steric conflict, indicating that this conformation represents an assembly-competent form. The PSAM retained high conformational stability, suggesting that the flat beta-strand of the Ile(5) stretch primed for self-assembly is a low-energy conformation of the Ile(5) stretch and rationalizing its high propensity for self-assembly. The ability of the PSAM to "solubilize" an otherwise insoluble peptide stretch suggests the potential of the PSAM approach to the characterization of self-assembling peptides.
富含β-折叠的自组装是多肽的一种主要结构类型，但对其原子结构和生物物理性质仍知之甚少。肽自组装体结构和生物物理研究的主要障碍包括其不溶性和组成不均一性。我们基于伯氏疏螺旋体表面蛋白A的单层β-折叠开发了一种模型系统，称为肽自组装模拟物（PSAM）。PSAM能够在水溶性蛋白中捕获一定数量的类似自组装的肽重复序列，从而使结构和能量研究成为可能。在这项工作中，我们将PSAM方法扩展到一个高度疏水的肽序列。我们表明，一种在水溶液中不溶且形成富含β-折叠自组装体的五聚异亮氨酸肽（Ile(5)），能够以一种自组装形式被捕获在PSAM支架内。1.1埃的晶体结构表明，Ile(5)片段在这个扁平的β-折叠中形成了一条高度规则的β-链。用Ile(5)肽段晶体结构的多个拷贝构建的自组装模型没有显示出空间冲突，表明这种构象代表一种具有组装能力的形式。PSAM保持了高构象稳定性，这表明为自组装做好准备的Ile(5)片段的扁平β-链是Ile(5)片段的低能量构象，并解释了其高度的自组装倾向。PSAM“溶解”原本不溶的肽段的能力表明了PSAM方法在自组装肽表征方面的潜力。
