Scheibel T, Neuhofen S, Weikl T, Mayr C, Reinstein J, Vogel P D, Buchner J
Institut für Biophysik und physikalische Biochemie, Universität Regensburg, 93040 Regensburg, Germany.
J Biol Chem. 1997 Jul 25;272(30):18608-13. doi: 10.1074/jbc.272.30.18608.
Hsp90 is one of the most abundant proteins in the cytosol of eukaryotic cells. Under physiological conditions Hsp90 has been shown to play a major role in several specific signaling pathways, including maturation of various kinases and maintenance of steroid receptors in an activable state. It is well established that the level of Hsp90 increases severalfold under stress conditions, and it has been shown that the chaperone function of Hsp90 is ATP-independent. Although yeast Hsp90 does not bind ATP, as determined by a number of methods monitoring tight binding, ATP-dependent functions of Hsp90 in the presence of co-factors and elevated temperatures are still under discussion. Here, we have reinvestigated ATP-binding properties and ATPase activity of human Hsp90 under various conditions. We show that human Hsp90 does not bind ATP tightly and does not exhibit detectable ATPase activity. However, using electron spin resonance spectroscopy, weak binding of spin-labeled ATP analogues with half-maximal binding at 400 microM ATP was detected. The functional significance of this weak interaction remains enigmatic.
热休克蛋白90（Hsp90）是真核细胞胞质溶胶中含量最为丰富的蛋白质之一。在生理条件下，Hsp90已被证明在多种特定信号通路中发挥主要作用，包括各种激酶的成熟以及将类固醇受体维持在可激活状态。众所周知，在应激条件下Hsp90的水平会增加数倍，并且已经表明Hsp90的伴侣功能不依赖于ATP。尽管通过多种监测紧密结合的方法确定酵母Hsp90不结合ATP，但在存在辅助因子和高温的情况下Hsp90的ATP依赖性功能仍在讨论之中。在此，我们重新研究了在各种条件下人Hsp90的ATP结合特性和ATP酶活性。我们发现人Hsp90不紧密结合ATP，并且未表现出可检测到的ATP酶活性。然而，使用电子自旋共振光谱法，检测到自旋标记的ATP类似物在400微摩尔ATP时具有半最大结合的弱结合。这种弱相互作用的功能意义仍然不明。
