PDF(Pubmed)
Abstract：
The viral protein HBx is the key regulatory factor of the hepatitis B virus (HBV) and the main etiology for HBV-associated liver diseases, such as cirrhosis and hepatocellular carcinoma. Historically, HBx has defied biochemical and structural characterization, deterring efforts to understand its molecular mechanisms. Here we show that soluble HBx fused to solubility tags copurifies with either a [2Fe-2S] or a [4Fe-4S] cluster, a feature that is shared among five HBV genotypes. We show that the O2-stable [2Fe-2S] cluster form converts to an O2-sensitive [4Fe-4S] state when reacted with chemical reductants, a transformation that is best described by a reductive coupling mechanism reminiscent of Fe-S cluster scaffold proteins. In addition, the Fe-S cluster conversions are partially reversible in successive reduction-oxidation cycles, with cluster loss mainly occurring during (re)oxidation. The considerably negative reduction potential of the [4Fe-4S]2+/1+ couple (-520 mV) suggests that electron transfer may not be likely in the cell. Collectively, our findings identify HBx as an Fe-S protein with striking similarities to Fe-S scaffold proteins both in cluster type and reductive transformation. An Fe-S cluster in HBx offers new insights into its previously unknown molecular properties and sets the stage for deciphering the roles of HBx-associated iron (mis)regulation and reactive oxygen species in the context of liver tumorigenesis.
摘要：
病毒蛋白HBx是乙型肝炎病毒（HBV）的关键调控因子，是HBV相关肝病的主要病因，如肝硬化和肝细胞癌。历史上,HBx具有生化和结构特性，阻止努力了解其分子机制。在这里，我们显示可溶性HBx融合到溶解度标签与[2Fe-2S]或[4Fe-4S]簇，这是在五个HBV基因型之间共享的特征。我们表明，当与化学还原剂反应时，O2稳定的[2Fe-2S]团簇形式会转化为O2敏感的[4Fe-4S]状态，通过还原偶联机制最好地描述的转化，让人联想到Fe-S簇支架蛋白。此外,Fe-S团簇转化在连续的还原-氧化循环中是部分可逆的，团簇损失主要发生在(再)氧化过程中。[4Fe-4S]2+/1+对(-520mV)的相当大的负还原电势表明电子转移可能不可能在电池中发生。总的来说，我们的发现确定HBx为Fe-S蛋白与Fe-S支架蛋白在簇型和还原转化方面具有惊人的相似性。HBx中的Fe-S簇提供了对其先前未知的分子特性的新见解，并为破译HBx相关的铁（mis）调节和活性氧在肝脏肿瘤发生背景下的作用奠定了基础。
