The HBx protein from hepatitis B virus coordinates a redox-active Fe-S cluster

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Updated: Oct 4, 2025

Identifying Inhibitors of the HBx-DDB1 Interaction Using a Split Luciferase Assay System
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Identifying Inhibitors of the HBx-DDB1 Interaction Using a Split Luciferase Assay System

Published on: December 21, 2019

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Chie Ueda1, Michelle Langton1, Jiahua Chen1

  • 1Department of Biochemistry, Brandeis University, Waltham, Massachusetts, USA.

The Journal of Biological Chemistry
|February 12, 2022
PubMed

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.

Keywords:
hepatitis B virusironiron–sulfur proteinredoxscaffold protein

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