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Abstract：
αB-crystallin is an archetypical member of the small heat-shock proteins (sHSPs) vital for cellular proteostasis and mitigating protein misfolding diseases. Gaining insights into the principles defining their molecular organization and chaperone function have been hindered by intrinsic dynamic properties and limited high-resolution structural analysis. To disentangle the mechanistic underpinnings of these dynamical properties, we mutated a conserved IXI-motif located within the N-terminal (NT) domain of human αB-crystallin. This resulted in a profound structural transformation, from highly polydispersed caged-like native assemblies into a comparatively well-ordered helical fibril state amenable to high-resolution cryo-EM analysis. The reversible nature of the induced fibrils facilitated interrogation of functional effects due to perturbation of the NT-IXI motif in both the native-like oligomer and fibril states. Together, our investigations unveiled several features thought to be key mechanistic attributes to sHSPs and point to a critical significance of the NT-IXI motif in αB-crystallin assembly, dynamics and chaperone activity.
摘要：
αB-晶状体蛋白是小热休克蛋白（sHSPs）的原型成员，对细胞蛋白停滞和减轻蛋白质错误折叠疾病至关重要。固有的动态特性和有限的高分辨率结构分析阻碍了对定义其分子组织和伴侣功能的原理的了解。为了解开这些动力学特性的机械基础，我们突变了位于人αB-晶状体蛋白的N端（NT）结构域内的保守的IXI基序。这导致了深刻的结构转型，从高度多分散的笼状天然组件到相对有序的螺旋原纤维状态，适合高分辨率的低温EM分析。由于NT-IXI基序在天然样寡聚体和原纤维状态下的扰动，诱导的原纤维的可逆性质促进了功能作用的询问。一起,我们的研究揭示了被认为是sHSP的关键机械属性的几个特征，并指出了NT-IXI基序在αB-晶状体蛋白组装中的关键意义，动力学和伴侣活动。
