Cheetham M E, Jackson A P, Anderton B H
Department of Neuroscience, Institute of Psychiatry, London, England.
Eur J Biochem. 1994 Nov 15;226(1):99-107. doi: 10.1111/j.1432-1033.1994.tb20030.x.
The DnaJ family of molecular chaperones is characterized by the presence of a highly conserved 70-amino-acid J domain. Escherichia coli DnaJ interacts with the 70-kDa heat-shock protein (DnaK), in vitro, to stimulate the 70-kDa heat-shock protein ATPase activity and modify substrate binding. The conservation of the interaction of DnaJ-like proteins with the 70-kDa heat-shock proteins has been demonstrated for the yeast protein YDJ1, a protein that shows full domain conservation with E. coli DnaJ. Human neurone-specific DnaJ-like proteins, HSJ1a and HSJ1b, possess a J domain and a glycine/phenylalanine-rich region in common with E. coli DnaJ, although the overall amino acid identity is less than 23%. We have investigated, in vitro, the interaction of HSJ1a and HSJ1b with the mammalian brain constitutive 70-kDa heat-shock protein (hsc70). The weak intrinsic ATPase activity of the constitutive 70-kDa heat-shock protein is enhanced more than fivefold by stoichiometric amounts of both HSJ1a and HSJ1b. This enhancement is mediated by an increase in the rate of bound ATP hydrolysis, whereas the rate of ADP release is unaffected. HSJ1 proteins appear to regulate the affinity of the 70-kDa constitutive heat-shock protein for the permanently unfolded substrate, carboxymethylated alpha-lactalbumin. A recent report [Palleros, D. R., Reid, K. L., Shi, L., Welch, W. J. & Fink, A. L. (1993) Nature 365, 664-666] has suggested that substrate release by 70-kDa heat-shock proteins requires a conformational change in these proteins induced by K+ in concert with ATP binding. In the presence of ATP, HSJ1 proteins reduce 70-kDa constitutive heat-shock protein/carboxymethylated alpha-lactalbumin complex formation both in the presence and absence of K+. This suggests that HSJ1 proteins induce a conformational change in the 70-kDa constitutive heat-shock protein that can mimic the effect mediated by K+ and therefore modulate 70-kDa heat-shock protein substrate release by another mechanism rather than merely stimulating the 70-kDa heat-shock protein ATPase activity. As HSJ1 proteins have limited similarity to DnaJ, we suggest that this action is being mediated by the J domain alone, and that this modulation of 70-kDa heat-shock-protein substrate binding will be common to all proteins that contain a J domain.
分子伴侣的DnaJ家族的特点是存在一个高度保守的70个氨基酸的J结构域。大肠杆菌DnaJ在体外与70 kDa热休克蛋白（DnaK）相互作用，以刺激70 kDa热休克蛋白的ATP酶活性并改变底物结合。酵母蛋白YDJ1已证明与70 kDa热休克蛋白相互作用的保守性，该蛋白与大肠杆菌DnaJ具有完全的结构域保守性。人类神经元特异性的类DnaJ蛋白HSJ1a和HSJ1b与大肠杆菌DnaJ一样，都具有一个J结构域和一个富含甘氨酸/苯丙氨酸的区域，尽管总体氨基酸同一性小于23%。我们在体外研究了HSJ1a和HSJ1b与哺乳动物脑组成型70 kDa热休克蛋白（hsc70）的相互作用。化学计量的HSJ1a和HSJ1b都能使组成型70 kDa热休克蛋白微弱的内在ATP酶活性增强超过五倍。这种增强是由结合的ATP水解速率增加介导的，而ADP释放速率不受影响。HSJ1蛋白似乎调节70 kDa组成型热休克蛋白对永久未折叠底物羧甲基化α-乳白蛋白的亲和力。最近的一份报告[帕勒罗斯，D.R.，里德，K.L.，施，L.，韦尔奇，W.J.和芬克，A.L.（1993年）《自然》365，664 - 666]表明，70 kDa热休克蛋白释放底物需要K +与ATP结合共同诱导这些蛋白发生构象变化。在有ATP存在的情况下，无论有无K +，HSJ1蛋白都会减少70 kDa组成型热休克蛋白/羧甲基化α-乳白蛋白复合物的形成。这表明HSJ1蛋白会诱导70 kDa组成型热休克蛋白发生构象变化，这种变化可以模拟K +介导的效应，因此通过另一种机制调节70 kDa热休克蛋白底物的释放，而不仅仅是刺激70 kDa热休克蛋白的ATP酶活性。由于HSJ1蛋白与DnaJ的相似性有限，我们认为这种作用仅由J结构域介导，并且这种对70 kDa热休克蛋白底物结合的调节对于所有含有J结构域的蛋白来说是共同的。
