Hernández M Patricia, Chadli Ahmed, Toft David O
Department of Biochemistry and Molecular Biology, Mayo Graduate School, Mayo Clinic, Rochester, Minnesota 55905, USA.
J Biol Chem. 2002 Apr 5;277(14):11873-81. doi: 10.1074/jbc.M111445200. Epub 2002 Jan 23.
The progesterone receptor (PR) can be isolated in its native conformation able to bind hormone, yet its ligand-binding domain rapidly loses its activity at elevated temperature. However, an in vitro chaperoning system consisting of five proteins (HSP40, HSP70, HOP, HSP90, and p23) with ATP is capable of restoring this function. The first step of this chaperoning mechanism is usually thought to be the binding of HSP70 to PR. Our findings here show that the binding of HSP40 to PR is, instead, the first step. HSP40 binding occurred rapidly and was not dependent on ATP or other proteins. The stoichiometry of HSP40 to native PR in these complexes was approximately 1:1. HSP40 bound specifically and with a high affinity to native PR (K(d) = 77 nm). The binding of HSP40 to PR was sustained and did not interact in the highly dynamic fashion that has been observed previously for HSP90 in this system. The HSP40 small middle dotPR complex could be isolated as a functional unit that could, after the addition of the other chaperones, progress to a PR complex capable of hormone binding. These results indicate that HSP40 initiates the entry of PR into the HSP90 pathway.
孕激素受体（PR）能够以其天然构象被分离出来并能够结合激素，然而其配体结合结构域在温度升高时会迅速丧失活性。但是，由五种蛋白质（热休克蛋白40（HSP40）、热休克蛋白70（HSP70）、热休克蛋白组织蛋白（HOP）、热休克蛋白90（HSP90）和p23）与三磷酸腺苷（ATP）组成的体外伴侣系统能够恢复这种功能。这种伴侣机制的第一步通常被认为是HSP70与PR的结合。我们在此的研究结果表明，相反，HSP40与PR的结合才是第一步。HSP40的结合迅速发生，且不依赖于ATP或其他蛋白质。在这些复合物中，HSP40与天然PR的化学计量比约为1:1。HSP40特异性且高亲和力地结合天然PR（解离常数（K(d)） = 77纳米）。HSP40与PR的结合持续存在，并且不像此前在该系统中观察到的HSP90那样以高度动态的方式相互作用。HSP40·PR复合物可以作为一个功能单元被分离出来，在添加其他伴侣蛋白后，它能够发展成为一个能够结合激素的PR复合物。这些结果表明，HSP40启动了PR进入HSP90途径的过程。
