Brenner Joel Cyrille, Zirden Linda Charlotte, Buzuk Lana, Almeida-Hernandez Yasser, Radzuweit Lea, Diamantino Joao, Kaschani Farnusch, Kaiser Markus, Sanchez-Garcia Elsa, Poepsel Simon, Hellerschmied Doris
Department of Mechanistic Cell Biology, Center of Medical Biotechnology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany.
Center for Molecular Medicine Cologne (CMMC), Faculty of Medicine and University Hospital, University of Cologne, Cologne, Germany.
Nat Struct Mol Biol. 2025 Jul 14. doi: 10.1038/s41594-025-01619-0.
Hsp70 and Hsp90 chaperones and their regulatory cochaperones are critical for maintaining protein homeostasis. Glucose-regulated protein 94 (GRP94), the sole Hsp90 chaperone in the secretory pathway of mammalian cells, is essential for the maturation of important secretory and transmembrane proteins. Without the requirement of cochaperones, the Hsp70 protein BiP controls regulatory conformational changes of GRP94, the structural basis of which has remained elusive. Here we biochemically and structurally characterize the formation of a BiP-GRP94 chaperone complex and its transition to a conformation expected to support the loading of substrate proteins from BiP onto GRP94. BiP initially binds to the open GRP94 dimer through an interaction interface that is conserved among Hsp70 and Hsp90 paralogs. Subsequently, binding of a second BiP protein stabilizes a semiclosed GRP94 dimer, thereby advancing the chaperone cycle. Our findings highlight a fundamental mechanism of direct Hsp70-Hsp90 cooperation, independent of cochaperones.
热休克蛋白70（Hsp70）和热休克蛋白90（Hsp90）伴侣蛋白及其调节性共伴侣蛋白对于维持蛋白质稳态至关重要。葡萄糖调节蛋白94（GRP94）是哺乳动物细胞分泌途径中唯一的Hsp90伴侣蛋白，对重要分泌蛋白和跨膜蛋白的成熟至关重要。热休克蛋白70家族的结合免疫球蛋白蛋白（BiP）无需共伴侣蛋白的参与，即可控制GRP94的调节性构象变化，其结构基础仍不清楚。在此，我们通过生物化学和结构分析，对BiP-GRP94伴侣蛋白复合物的形成及其向预期构象的转变进行了表征，该构象有望支持底物蛋白从BiP转移到GRP94上。BiP最初通过热休克蛋白70和热休克蛋白90同源物之间保守的相互作用界面与开放的GRP94二聚体结合。随后，第二个BiP蛋白的结合稳定了半封闭的GRP94二聚体，从而推进了伴侣蛋白循环。我们的研究结果突出了一种直接的热休克蛋白70-热休克蛋白90合作的基本机制，该机制独立于共伴侣蛋白。
