USE OF DESIGNED PEPTIDES TO PROBE BETA-SHEET FOLDING

我们建议使用多肽模型系统来解释β-折叠构象稳定性的起源。这项工作将利用我们实验室和其他实验室最近的进展，这些实验室已经确定了诱导小肽在水溶液中采用反平行β-折叠构象的一般策略。这种方法的重点是β-发夹折叠单元，在该单元中，两条链通过一个短环连接。我们将使用基于发夹的实验设计来实现四个具体目标。(1)我们将使用模型系统来探索反平行的β-折叠二级结构，包括协作性和链间侧链-侧链相互作用对构象稳定性的贡献。(2)我们将用从我们的反平行贝塔-折叠工作和其他工作人员的结果扩展而来的模型系统来检验平行贝塔-折叠稳定性的起源。(3)我们将从我们的β-折叠二级结构模型中建立一个新的三级结构基序，其中多聚脯氨酸II(PPII)螺旋包装在双链β-折叠的一个面上。该基序可能表现出较高的构象稳定性，残基相对较少。拟议的BetabetaPPII基序将提供一个独特的机会，在三级结构水平上确定合作性的起源。(4)我们将使用发夹结构来评估多肽链和非肽低聚物之间的相互作用。最终，我们希望识别非天然的寡聚体，这些寡聚体可以像Beta片状一样结合到延伸的多肽链上，从而扰乱有害的蛋白质聚集过程。拟议的Beta-Sheet模型研究将通过提供对许多实验室已报道的广泛的α-螺旋模型研究的补充，增强我们对蛋白质折叠偏好的理解。我们的结果也应该有助于蛋白质设计和工程努力，以及淀粉样蛋白疾病化学疗法的发展。

We propose to use peptide model systems to elucidate the origins of beta-sheet conformational stability. This effort will take advantage of recent advances from our laboratory and from others that have identified a general strategy for inducing small peptides to adopt antiparallel beta-sheet conformations in aqueous solution. This approach focuses on the beta-hairpin folding unit, in which two strands are connected by a short loop. We will use hairpin-based experimental designs to achieve four specific aims. (1) We will use model systems to probe antiparallel beta-sheet secondary structure, including the contributions of cooperativity and interstrand sidechain-sidechain interactions to conformational stability. (2) We will examine the origins of parallel beta-sheet stability with model systems developed by extention from our antiparallel beta-sheet work and from results of other workers. (3) We will build from our beta-sheet secondary structure models to create a new tertiary structural motif, in which a polyproline II (PPII) helix packs against one face of a two-stranded beta-sheet. This motif is likely to display high conformational stability with relatively few residues. The proposed betabetaPPII motif will provide a unique opportunity to determine the origins of cooperativity at the tertiary structure level. (4) We will use the hairpin architecture to evaluate interactions between peptide strands and non-peptide oligomers. Ultimately, we would like to identify unnatural oligomers that can bind in beta-sheet-like fashion to an extended peptide strand, and thereby disrupt deleterious protein aggregation processes. The proposed beta-sheet model studies will enhance our understanding of protein folding preferences by providing a complement to the extensive alpha-helix model studies that have been reported from many laboratories. Our results should also contribute to protein design and engineering efforts, and to the development of chemotherapies for amyloid diseases.