The Integrity of the Intradimer Interface of the Hepatitis B Virus Capsid Protein Dimer Regulates Capsid Self-Assembly
Zhongchao Zhao, Joseph Che-Yen Wang, Carolina Perez Segura, Jodi A Hadden-Perilla, Adam Zlotnick
PMID: 32459465 DOI: 10.1021/acschembio.0c00277
Abstract
During the hepatitis B virus lifecycle, 120 copies of homodimeric capsid protein assemble around a copy of reverse transcriptase and viral RNA and go on to produce an infectious virion. Assembly needs to be tightly regulated by protein conformational change to ensure symmetry, fidelity and reproducibility. Here we show that structures at the intradimer interface regulate conformational changes at the distal interdimer interface and so regulate assembly. A pair of interacting charged residues, D78 from each monomer, conspicuously located at the top of a four-helix bundle that forms the intradimer interface, were mutated to serine to disrupt communication between the two monomers. The mutation slowed assembly and destabilized dimer to thermal and chemical denaturation. Mutant dimers showed evidence of transient partial unfolding based on appearance of new proteolytically-sensitive sites. Though mutant dimer was less stable, the resulting capsids were as stable as wildtype, based on assembly and thermal denaturation studies. Cryo-EM image reconstructions of capsid indicated that the subunits adopted an "open" state more usually associated with free dimer and that the spike tips were either disordered or highly flexible. Molecular dynamics simulations provide mechanistic explanations for these results, suggesting that D78 stabilizes helix 4a, which forms part of the intradimer interface, by capping its N-terminus and hydrogen-bonding to nearby residues, whereas the D78S mutation disrupts these interactions, leading to partial unwinding of helix 4a. This in turn weakens the connection from helix 4 and the intradimer interface to helix 5, which forms the interdimer interface. . 作者: StephenW 时间: 2020-5-29 13:44