Single-conformation spectroscopy of isolated peptides and synthetic foldamers

在该奖项中，由化学系化学结构，动力学和机制计划资助，普渡大学的Timothy Zwier教授及其研究生和本科生正在进行一系列模型肽，合成折叠体和肽聚集体的构象偏好和激光诱导异构化的实验研究，研究要么作为孤立的分子在超音速膨胀冷却，或作为离子冷却到10 K的低温冷却离子阱。中性肽和折叠体正在研究使用激光诱导荧光（LIF），质量分辨共振双光子电离（R2 PI），红外-紫外和紫外-紫外空穴燃烧方法，以确定构象异构体的数量，并获得其单一构象的红外和紫外光谱。从这些光谱中，研究人员推断出优选的分子内氢键排列，发现其独特的光谱特征，提供计算准确性的基准测试，并为量化大分子中非键相互作用的新兴方法提供测试平台。在溶液中形成松散螺旋的富含脯氨酸的α-肽正在以分离的形式进行研究，以确定它们在不存在溶剂的情况下的固有构象偏好。合成的折叠体组成的几种类型的约束肽，合作制备的Gellman组，正在研究如何延长的肽骨架结合从环状残基的限制，影响构象的偏好。在将这些研究扩展到包括离子的过程中，Zwier教授和他的团队正在使用一种新构建的多级质谱仪，该质谱仪包含一个低温冷却的离子阱，能够使用光碎片光谱法对较大的肽和肽聚集体进行单一构象光谱分析。这里的重点是已知在溶液中形成原型二级结构的较长肽序列。 最后，两个模型肽六聚体（NNQQNY和VENUL）组成的序列，在淀粉样蛋白原纤维形成中发挥关键作用，正在研究作为prefibrillar聚集体（寡聚体离子含有2-12个单体），以获得独特的光谱特征的交叉β-折叠形成的早期阶段。该研究项目通过提供重要的天然和合成结构支架的深刻实验测试来影响整个社会，这可以帮助下一代量子化学，力场，光谱和动力学方法的理论发展。具体目标涉及重要的生物物理问题。富含脯氨酸的α-肽是非结构化蛋白质片段的模型。合成折叠体形成独特的结构支架，设计用于与与广泛的生物医学和药物发现应用相关的特定生物受体相互作用。可溶性前纤维寡聚体在淀粉样蛋白疾病发病机制中的可能作用使其成为详细结构表征的重要靶点。

In this award, funded by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Timothy Zwier of Purdue University and his graduate and undergraduate students are carrying out experimental studies of the conformational preferences and laser-induced isomerization of a series of model peptides, synthetic foldamers, and peptide aggregates, studied either as isolated molecules cooled in a supersonic expansion or as ions cooled to 10K in a cryo-cooled ion trap. Neutral peptides and foldamers are being studied using laser-induced fluorescence (LIF), mass-resolved resonant two-photon ionization (R2PI), IR-UV and UV-UV hole-burning methods to determine the number of conformational isomers present and obtain their single-conformation infrared and ultraviolet spectra. From these spectra, the researchers deduce the preferred intramolecular H-bonding arrangements, discover their unique spectral signatures, provide benchmark tests of the accuracy of calculations, and provide a test bed for emerging methods for quantifying non-bonding interactions in large molecules. Proline-rich alpha-peptides that form loose helices in solution are being studied in isolated form to determine their inherent conformational preferences in the absence of solvent. Synthetic foldamers composed of several types of constrained peptides, prepared collaboratively by the Gellman group, are being studied to test how elongation of the peptide backbone in combination with constraints from cyclic residues, affects the conformational preferences. In expanding these studies to include ions, Professor Zwier and his team are using a newly constructed multi-stage mass spectrometer that incorporates a cryocooled ion trap capable of carrying out single-conformation spectroscopy on larger peptides and peptide aggregates, using photofragment spectroscopy. Here the focus is on longer peptide sequences known in solution to form prototypical secondary structures. Finally, two model peptide hexamers (NNQQNY and VEALYL) composed of sequences that play key roles in amyloid fibril formation, are under investigation as prefibrillar aggregates (oligomer ions containing 2-12 monomers), with the goal of obtaining unique spectroscopic signatures of the early stages of interdigitized beta-sheet formation. This research project impacts society at large by providing incisive experimental tests of important natural and synthetic structural scaffolds, which can aid theoretical development of next-generation quantum chemical, force field, spectroscopic, and dynamics methods. Specific targets touch on important biophysical problems. Proline-rich alpha-peptides are models for unstructured protein segments. Synthetic foldamers form unique structural scaffolds designed to interact with specific biological receptors of relevance to a wide range of biomedical and drug-discovery applications. The probable role of soluble prefibrillar oligomers in amyloid disease pathogenesis makes them important targets for detailed structural characterization.