USE OF DESIGNED PEPTIDES TO PROBE BETA-SHEET FOLDING

我们建议使用肽模型系统来阐明β -片构象稳定性的起源。这项工作将利用我们实验室和其他实验室的最新进展，这些进展已经确定了在水溶液中诱导小肽采用反平行β -片构象的一般策略。这种方法的重点是β发夹折叠单元，其中两条链由一个短环连接。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测反平行β -片二级结构，包括协同性和链间侧链-侧链相互作用对构象稳定性的贡献。(2)我们将通过推广我们的反平行β -片工作和其他工作者的结果而开发的模型系统来研究平行β -片稳定性的起源。(3)我们将从我们的β -sheet二级结构模型中构建一个新的三级结构基序，其中一个聚脯氨酸II （PPII）螺旋围绕着一个两链β -sheet的一个面。该基序可能具有较高的构象稳定性和相对较少的残基。提出的betabetaPPII基序将提供一个独特的机会来确定三级结构水平上合作的起源。(4)我们将使用发夹结构来评估肽链和非肽寡聚物之间的相互作用。最终，我们希望鉴定出能够以β -薄片样方式结合到延伸肽链上的非天然低聚物，从而破坏有害的蛋白质聚集过程。提出的β -薄片模型研究将通过为许多实验室报道的广泛的α -螺旋模型研究提供补充，增强我们对蛋白质折叠偏好的理解。我们的研究结果也将有助于蛋白质设计和工程的努力，以及淀粉样蛋白疾病化疗的发展。

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.