Molecular Mechanism for the Chaperone Activity of Hsp90

热休克蛋白90是一种分子伴侣，有助于新合成的蛋白质的折叠，并维持细胞内蛋白质的折叠状态。Hsp 90在从细菌到人类的许多细胞类型的细胞质和细胞核中丰富，并且参与许多生化过程。与典型的伴侣蛋白相比，Hsp 90的伴侣蛋白功能的作用模式是独特的，因为它结合部分或完全折叠的蛋白质，而不是未折叠蛋白质的疏水区域。Hsp 90协助许多“客户”蛋白的折叠，包括突变、过表达或失调形式的信号蛋白，如激酶、类固醇受体和转录因子，强调了Hsp 90在信号传导中的关键作用。Hsp 90的分子机制的当前观点是客户蛋白激活涉及与特定Hsp 90构象的结合，其中分子伴侣以ATP依赖性方式循环通过各种构象。热休克蛋白90的构象循环，部分或完全折叠的蛋白质的结合，以及辅分子伴侣的结合之间的关系尚未完全理解。Hsp 90功能的关键参与者是辅助分子伴侣Aha 1，其与Hsp 90相互作用，加速ATP酶活性，并最终帮助激活激酶。如何建立分子伴侣的功能机制是热休克蛋白90研究领域的一个突出问题。为此，我们推导了一个物理化学动力学模型来描述周期中各种配体、蛋白质、蛋白质-蛋白质和蛋白质-配体复合物浓度的时间依赖性变化。这个基本的物理模型包括实验确定的蛋白质-蛋白质，和蛋白质-配体缔合速率，以及ATP水解的限速催化步骤。此外，该模型包括热休克蛋白90的相互作用与ATP酶激活辅助分子Aha 1，和热休克蛋白90的相互作用与折叠中间体从客户端蛋白质之间的平衡折叠，中间体，和未折叠状态。我们计划将来自动力学模型的见解与NMR光谱学和生物化学测定相结合，以更好地了解Hsp 90的分子功能。对该机制的详细了解可以深入了解细胞中伴侣蛋白的正常和基本功能。该物理化学动力学模型代表了我们对伴侣Hsp 90的理解的新合成。在分子伴侣领域中，有相当大的兴趣，关于Hsp 90的相对水平的功能及其在细胞中通过辅分子伴侣的激活来控制蛋白质的功能，或抑制控制信号传导途径的激酶的功能。物理化学动力学模型可以应用于此类问题，以预测辅伴侣如何调节Hsp 90的生物活性。

Hsp90 is a molecular chaperone that assists the folding of newly synthesized proteins, and the maintenance of the folded state of proteins within cells. Hsp90 is abundant in the cytoplasm and nucleus in many cell types, ranging from bacterial to human, and is involved in numerous biochemical processes. The mode of action for the chaperone function of Hsp90 is unique compared to typical chaperones, as it binds partially or fully folded proteins, not the hydrophobic regions of unfolded proteins. Hsp90 assists the folding of a number of “client” proteins that include mutant, overexpressed, or misregulated forms of signaling proteins such as kinases, steroid receptors, and transcription factors, underscoring the key role for Hsp90 in signalling. The current view of the molecular mechanism for Hsp90 is that client protein activation involves binding to specific Hsp90 conformations, wherein the chaperone cycles through the various conformations in an ATP-dependent manner. The relationship between the conformational cycling Hsp90, the binding of partially, or fully folded proteins, and the binding of co-chaperones is not yet fully understood. A key player in the function of Hsp90 is the co-chaperone Aha1, which interacts with Hsp90, accelerates the ATPase activity, and ultimately helps activate kinases. It remains an outstanding problem in the Hsp90 field to develop a mechanism to describe the function of the chaperone. To that end, we derived a physicochemical kinetic model to describe the time dependent changes in the concentrations of the various ligands, proteins, protein-protein, and protein-ligand complexes for the cycle. This fundamental physical model includes experimentally determined protein-protein, and protein-ligand association rates, and the rate limiting catalytic step for ATP hydrolysis. Furthermore, the model includes the interaction of Hsp90 with the ATPase activating co-chaperone Aha1, and the interaction of Hsp90 with a folding intermediate from a client protein in equilibrium between folded, intermediate, and unfolded states. We plan to blend insights derived from the kinetic model with a combination of NMR spectroscopy and biochemical assays to better understand the molecular function of Hsp90. A detailed understanding of the mechanism can yield insights into the normal and essential function of chaperones in cells. This physicochemical kinetic model represents a novel synthesis of our understanding of the chaperone Hsp90. There is considerable interest in the chaperone field regarding the function of relative levels of Hsp90 and its activation by cochaperones in cells to control the function of proteins, or to suppress the function of kinases that control signaling pathways. The physicochemical kinetic model can be applied to such problems to predict how co-chaperones regulate the biological activity of Hsp90.**