Johnson B D, Schumacher R J, Ross E D, Toft D O
Department of Biochemistry and Molecular Biology, Mayo Graduate School, Rochester, Minnesota 55905, USA.
J Biol Chem. 1998 Feb 6;273(6):3679-86. doi: 10.1074/jbc.273.6.3679.
Hop is a 60-kDa protein characterized by its ability to bind the two chaperones, hsp70 and hsp90. We have tested the function of Hop using an assay for the refolding of denatured firefly luciferase. We show that Hop is involved in the process of refolding thermally denatured firefly luciferase in rabbit reticulocyte lysate. Hop also stimulates refolding by hsp70 and Ydj-1 in a purified refolding system. Hsp90 can also stimulate refolding, and optimal refolding is observed in the presence of both Hop and hsp90. Similar stimulation was observed when Hop was replaced by its yeast homolog Sti1. In assays of the binding of Hop to hsp70 and hsp90, Hop preferentially forms a complex with ADP-bound hsp70, and this process is unaffected by the presence of hsp90. Hop does not alter the ATPase activity or the rate of ADP dissociation of hsp70. Hop also appears to bind to the ADP-bound form of hsp90, blocking the ATP-dependent conversion of hsp90 to a form capable of interacting with p23. Conversely, once p23 is bound to hsp90, Hop binding is diminished. These results confirm that Hop provides a physical link between hsp70 and hsp90 and also indicate that Hop modulates the activities of both of these chaperone proteins.
Hop是一种60 kDa的蛋白质，其特点是能够结合两种伴侣蛋白hsp70和hsp90。我们使用变性萤火虫荧光素酶复性检测法测试了Hop的功能。我们发现Hop参与了兔网织红细胞裂解物中热变性萤火虫荧光素酶的复性过程。在纯化的复性系统中，Hop还能刺激hsp70和Ydj-1介导的复性。Hsp90也能刺激复性，并且在同时存在Hop和hsp90时观察到最佳复性效果。当Hop被其酵母同源物Sti1取代时，也观察到了类似的刺激作用。在Hop与hsp70和hsp90的结合检测中，Hop优先与结合ADP的hsp70形成复合物，并且这一过程不受hsp90存在的影响。Hop不会改变hsp70的ATP酶活性或ADP解离速率。Hop似乎还能结合结合ADP的hsp90形式，阻止hsp90依赖ATP转化为能够与p23相互作用的形式。相反，一旦p23与hsp90结合，Hop的结合就会减少。这些结果证实Hop在hsp70和hsp90之间提供了物理联系，并且还表明Hop调节了这两种伴侣蛋白的活性。
