Kinetically-stabilized mesoscopic protein aggregates

人们普遍认为，蛋白质的氨基酸序列经过优化，使分子始终折叠成独特、稳定的3D形状，同时避免与其他生物分子聚集。然而，这种观点过于简单化了。一方面，许多蛋白质不是整体结构；例如，肌红蛋白必须变形才能让氧气进入。另一方面，在某些条件下，蛋白质可能以错误折叠的构象聚集成淀粉样纤维。这些现象虽然很复杂，但仍然可以从热力学的角度来理解。在足够大的自然状态熵下，蛋白质是可变形的，而淀粉样纤维是通过纤维内的多个氨基酸接触来稳定的。最近在几种蛋白质溶液中发现的介观液体状聚集体，包括溶菌酶、血红蛋白和-结晶蛋白，则鲜为人知。这些团簇是蛋白质晶体的重要成核位点。这个项目的目的是测试一个微观假设的介观簇的形成，其中簇的形成是由长寿命的蛋白质复合物稳定在高密度。异常大的簇大小源于复合物的长寿命，这反过来又归功于它们的稳定性组成蛋白质分子的构象自由。所提出的机制的一个关键组成部分是蛋白质在结合之前部分展开，甚至可能经历结构域交换，从而蛋白质片段结合到不同蛋白质上的互补片段。pi将采用动态光散射、布朗显微镜、酰胺交换核磁共振和理论模型的组合，在几种系统中测试这种机制，包括蛋白质barnase、RNase a、血红蛋白、胰岛素和溶菌酶。这项研究是一个理论物理化学家和实验化学工程师跨学科的努力。将进行广泛的物理化学和生物化学测量和物理建模的综合，以解决这个难题；该结果有望产生对生物过程的基本理解，并为制造新材料提供新的途径。研究生、本科生和高中生将接受物理、化学和生物的交叉训练。ppi所在的休斯顿大学是美国种族最多样化的研究型大学之一，也是美国仅有的三所为西班牙裔服务的大学之一。将利用与当地作家和电台名人的现有合作来宣传这项研究的社会效益。本项目由分子与细胞生物科学部分子生物物理集群和物理部生命系统物理学项目共同支持。

It is generally accepted that a protein's amino acid sequence is optimized so that the molecule consistently folds into a unique, stable 3D shape while avoiding aggregation with other biomolecules. Yet this view is overly simplistic. On the one hand, many proteins are not monolithic structures; for instance, myoglobin must reliably deform to let in oxygen. On the other hand, under certain conditions, proteins may aggregate into amyloid fibers while in a misfolded conformation. Although very complex, these phenomena can still be understood thermodynamically. Proteins are deformable given a sufficiently large native state entropy, while amyloid fibers are stabilized by multiple amino acid contacts within the fiber. Much less understood are the mesoscopic liquid-like aggregates recently found in several protein solutions, including lysozyme, hemoglobin, and gamma-crystallin. These clusters are important as nucleation sites for protein crystals. The objective of this project is to test a microscopic hypothesis for the formation of the mesoscopic clusters by which the clusters result from the formation of long-lived protein complexes stabilized at high densities. The unusually large cluster size stems from the long lifetime of the complexes, which in turn owe their stability to the conformational freedom of constituent protein molecules. A key component of the proposed mechanism is that proteins partially unfold prior to binding and may even undergo domain swapping, whereby protein segments bind to complimentary segments on a different protein. The PIs will employ a combination of dynamic light scattering, Brownian microscopy, amide exchange NMR, and theoretical modeling to test this mechanism in several systems, including proteins barnase, RNase A, hemoglobin, insulin, and lysozyme.This research is a multidisciplinary effort by a theoretical physical chemist and experimental chemical engineer. A synthesis of a wide range of physicochemical and biochemical measurements and physical modeling will be undertaken to tackle this difficult problem; the outcome is expected to produce fundamental understanding of biological processes and provide new avenues for making new materials. Graduate, undergraduate, and high school students will be trained at the interface between physics, chemistry, and biology. The home institution of the PIs, the University of Houston, is one of the most ethnically diverse research universities in the nation, and is one of only three Hispanic-Serving Institutions in the US. Existing collaborations with local writers and radio personalities will be utilized to publicize the societal benefits of the research. This project is jointly supported by the Molecular Biophysics Cluster in the Division of Molecular and Cellular Biosciences and the Physics of Living Systems Program in the Physics Division.