The Hsp90 chaperone promotes folding and activation of hundreds of client proteins in the cell through an ATP-dependent conformational cycle guided by distinct cochaperone regulators. The FKBP51 immunophilin binds Hsp90 with its tetratricopeptide repeat (TPR) domain and catalyzes peptidyl-prolyl isomerase (PPIase) activity during folding of kinases, nuclear receptors, and tau. Here we determined the cryoelectron microscopy (cryo-EM) structure of the human Hsp90:FKBP51:p23 complex to 3.3 Å, which, together with mutagenesis and crosslinking analyses, reveals the basis for cochaperone binding to Hsp90 during client maturation. A helix extension in the TPR functions as a key recognition element, interacting across the Hsp90 C-terminal dimer interface presented in the closed, ATP conformation. The PPIase domain is positioned along the middle domain, adjacent to Hsp90 client binding sites, whereas a single p23 makes stabilizing interactions with the N-terminal dimer. With this architecture, FKBP51 is positioned to act on specific client residues presented during Hsp90-catalyzed remodeling.

Hsp90 伴侣通过由不同的伴侣调节剂引导的 ATP 依赖性构象循环促进细胞中数百种客户蛋白的折叠和激活。FKBP51 亲免素将 Hsp90 与其四肽重复 (TPR) 结构域结合，并在激酶、核受体和 tau 折叠过程中催化肽基-脯氨酰异构酶 (PPIase) 活性。在这里，我们确定了人类 Hsp90:FKBP51:p23 复合物的冷冻电子显微镜 (cryo-EM) 结构为 3.3 Å，结合诱变和交联分析，揭示了在客户成熟期间 cochaperone 与 Hsp90 结合的基础。TPR 中的螺旋延伸作为关键识别元件发挥作用，通过以封闭的 ATP 构象呈现的 Hsp90 C 末端二聚体界面相互作用。PPIase 结构域位于中间结构域，与 Hsp90 客户结合位点相邻，而单个 p23 与 N 端二聚体形成稳定的相互作用。借助这种架构，FKBP51 可以作用于在 Hsp90 催化的重塑过程中呈现的特定客户残基。