Demand J, Lüders J, Höhfeld J
ZMBH, Zentrum für Molekulare Biologie, Universität Heidelberg, Germany.
Mol Cell Biol. 1998 Apr;18(4):2023-8. doi: 10.1128/MCB.18.4.2023.
The modulation of the chaperone activity of the heat shock cognate Hsc70 protein in mammalian cells involves cooperation with chaperone cofactors, such as Hsp40; BAG-1; the Hsc70-interacting protein, Hip; and the Hsc70-Hsp90-organizing protein, Hop. By employing the yeast two-hybrid system and in vitro interaction assays, we have provided insight into the structural basis that underlies Hsc70's cooperation with different cofactors. The carboxy-terminal domain of Hsc70, previously shown to form a lid over the peptide binding pocket of the chaperone protein, mediates the interaction of Hsc70 with Hsp40 and Hop. Remarkably, the two cofactors bind to the carboxy terminus of Hsc70 in a noncompetitive manner, revealing the existence of distinct binding sites for Hsp40 and Hop within this domain. In contrast, Hip interacts exclusively with the amino-terminal ATPase domain of Hsc70. Hence, Hsc70 possesses separate nonoverlapping binding sites for Hsp40, Hip, and Hop. This appears to enable the chaperone protein to cooperate simultaneously with multiple cofactors. On the other hand, BAG-1 and Hip have recently been shown to compete in binding to the ATPase domain. Our data thus establish the existence of a network of cooperating and competing cofactors regulating the chaperone activity of Hsc70 in the mammalian cell.
哺乳动物细胞中热休克同源蛋白Hsc70伴侣活性的调节涉及与伴侣辅因子的协同作用，如Hsp40、BAG-1、Hsc70相互作用蛋白Hip以及Hsc70-Hsp90组织蛋白Hop。通过应用酵母双杂交系统和体外相互作用分析，我们深入了解了Hsc70与不同辅因子协同作用的结构基础。Hsc70的羧基末端结构域先前被证明可在伴侣蛋白的肽结合口袋上形成一个盖子，介导Hsc70与Hsp40和Hop的相互作用。值得注意的是，这两种辅因子以非竞争性方式结合到Hsc70的羧基末端，揭示了该结构域内Hsp40和Hop存在不同的结合位点。相比之下，Hip仅与Hsc70的氨基末端ATP酶结构域相互作用。因此，Hsc70拥有分别用于Hsp40、Hip和Hop的不重叠的结合位点。这似乎使伴侣蛋白能够同时与多种辅因子协同作用。另一方面，最近发现BAG-1和Hip在结合ATP酶结构域时存在竞争。因此，我们的数据证实了在哺乳动物细胞中存在一个由协同和竞争的辅因子组成的网络来调节Hsc70的伴侣活性。
