Biancalana Matthew, Makabe Koki, Koide Akiko, Koide Shohei
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
J Mol Biol. 2008 Oct 31;383(1):205-13. doi: 10.1016/j.jmb.2008.08.031. Epub 2008 Aug 22.
Though beta-rich self-assemblies comprise a major structural class of polypeptides, a detailed understanding of the determinants of their structure and stability is lacking. In particular, the roles of repetitive stretches of side chains running the long axis of these beta-sheets, termed "cross-strand ladders," remain poorly characterized due to the inherently insoluble and heterogeneous nature of self-assemblies. To overcome these experimental challenges, we have established a complementary experimental system termed "peptide self-assembly mimics" (PSAMs). The PSAMs capture a defined number of self-assembly-like peptide repeats within a soluble beta-rich protein, making structural and energetic studies possible. In this work, we investigated the role of cross-strand ladders containing aromatic residues, which are prominent in self-assembling peptides. A combination of solution data and high-resolution crystal structures revealed that a single cross-strand ladder consisting solely of Tyr significantly stabilized, rigidified, and flattened the PSAM beta-sheet. These characteristics would stabilize each beta-sheet layer of a self-assembly and direct sheet conformations compatible with lamination. Our results therefore provide a rationale for the abundance of aromatic amino acids in fibril-forming peptides and establish important roles of cross-strand Tyr ladders in the structure and stability of beta-rich peptide self-assemblies.
尽管富含β折叠的自组装体是多肽的主要结构类别，但对其结构和稳定性的决定因素仍缺乏详细了解。特别是，沿着这些β折叠长轴延伸的侧链重复片段（称为“跨链阶梯”）的作用，由于自组装体固有的不溶性和异质性，仍未得到充分表征。为了克服这些实验挑战，我们建立了一个互补的实验系统，称为“肽自组装模拟物”（PSAM）。PSAM在一种可溶性富含β折叠的蛋白质中捕获了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，我们研究了在自组装肽中突出的含芳香族残基的跨链阶梯的作用。溶液数据和高分辨率晶体结构的结合表明，仅由酪氨酸组成的单个跨链阶梯显著稳定、硬化并扁平化了PSAM的β折叠。这些特性将稳定自组装体的每个β折叠层，并引导与层压兼容的折叠构象。因此，我们的结果为成纤维肽中芳香族氨基酸的丰富性提供了理论依据，并确立了跨链酪氨酸阶梯在富含β折叠的肽自组装体的结构和稳定性中的重要作用。
