Molecular chaperones are key components of the cellular proteostasis network whose role includes the suppression of the formation and proliferation of pathogenic aggregates associated with neurodegenerative diseases. The molecular principles that allow chaperones to recognize misfolded and aggregated proteins remain, however, incompletely understood. To address this challenge, here we probe the thermodynamics and kinetics of the interactions between chaperones and protein aggregates under native solution conditions using a microfluidic platform. We focus on the binding between amyloid fibrils of α-synuclein, associated with Parkinson’s disease, to the small heat-shock protein αB-crystallin, a chaperone widely involved in the cellular stress response. We find that αB-crystallin binds to α-synuclein fibrils with high nanomolar affinity and that the binding is driven by entropy rather than enthalpy. Measurements of the change in heat capacity indicate significant entropic gain originates from the disassembly of the oligomeric chaperones that function as an entropic buffer system. These results shed light on the functional roles of chaperone oligomerization and show that chaperones are stored as inactive complexes which are capable of releasing active subunits to target aberrant misfolded species.

分子伴侣是细胞蛋白稳态网络的关键组成部分，其作用包括抑制与神经退行性疾病相关的致病聚集体的形成和增殖。然而，允许伴侣识别错误折叠和聚集蛋白质的分子原理仍未完全了解。为了应对这一挑战，我们在此使用微流体平台探索天然溶液条件下伴侣和蛋白质聚集体之间相互作用的热力学和动力学。我们专注于与帕金森病相关的 α-突触核蛋白的淀粉样蛋白原纤维与小热休克蛋白 αB-晶状体蛋白（一种广泛参与细胞应激反应的伴侣蛋白）之间的结合。我们发现αB-晶状体蛋白以高纳摩尔亲和力与α-突触核蛋白原纤维结合，并且这种结合是由熵而不是焓驱动的。对热容量变化的测量表明，显着的熵增益源于充当熵缓冲系统的低聚伴侣的分解。这些结果揭示了伴侣寡聚化的功能作用，并表明伴侣被储存为非活性复合物，能够释放活性亚基以靶向异常错误折叠的物种。