Zenthon Joanna F, Ness Frederique, Cox Brian, Tuite Mick F
Protein Science Group, Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom.
Eukaryot Cell. 2006 Feb;5(2):217-25. doi: 10.1128/EC.5.2.217-225.2006.
The molecular chaperone Hsp104 is not only a key component of the cellular machinery induced to disassemble aggregated proteins in stressed cells of Saccharomyces cerevisiae but also plays an essential role in the propagation of the [PSI+], [URE3], and [RNQ/PIN+] prions in this organism. Here we demonstrate that the fungal pathogen Candida albicans carries an 899-residue stress-inducible orthologue of Hsp104 (CaHsp104) that shows a high degree of amino acid identity to S. cerevisiae Hsp104 (ScHsp104). This identity is significantly lower in the N- and C-terminal regions implicated in substrate recognition and cofactor binding, respectively. CaHsp104 is able to provide all known functions of ScHsp104 in an S. cerevisiae hsp104 null mutant, i.e., tolerance to high-temperature stress, reactivation of heat-denatured proteins, and propagation of the [PSI+] prion. As also observed for ScHsp104, overexpression of CaHsp104 leads to a loss of the [PSI+] prion. However, unlike that of ScHsp104, CaHsp104 function is resistant to guanidine hydrochloride (GdnHCl), an inhibitor of the ATPase activity of this chaperone. These findings have implications both in terms of the mechanism of inhibition of Hsp104 by GdnHCl and in the evolution of the ability of fungal species to propagate prions.
分子伴侣Hsp104不仅是酿酒酵母应激细胞中诱导拆解聚集蛋白的细胞机制的关键组成部分，而且在该生物体中[PSI+]、[URE3]和[RNQ/PIN+]朊病毒的传播中也起着至关重要的作用。在此，我们证明真菌病原体白色念珠菌携带一种899个氨基酸残基的应激诱导型Hsp104直系同源物（CaHsp104），它与酿酒酵母Hsp104（ScHsp104）具有高度的氨基酸同一性。这种同一性在分别涉及底物识别和辅因子结合的N端和C端区域显著降低。CaHsp104能够在酿酒酵母hsp104缺失突变体中发挥ScHsp104的所有已知功能，即对高温应激的耐受性、热变性蛋白的重新激活以及[PSI+]朊病毒的传播。正如在ScHsp104中也观察到的那样，CaHsp104的过表达导致[PSI+]朊病毒的丧失。然而，与ScHsp104不同的是，CaHsp104的功能对盐酸胍（GdnHCl）具有抗性，盐酸胍是这种分子伴侣ATP酶活性的抑制剂。这些发现对于GdnHCl抑制Hsp104的机制以及真菌物种传播朊病毒能力的进化都具有重要意义。
