title: Structurally similar woodchuck and human hepadnavirus core proteins have distinctly different temperature dependences of assembly.
abstract: Woodchuck hepatitis virus (WHV), a close relative of human hepatitis B virus (HBV), has been a key model for disease progression and clinical studies. Sequences of the assembly domain of WHV and HBV core proteins (wCp149 and hCp149, respectively) have 65% identity, suggesting similar assembly behaviors. We report a cryo-electron microscopy (cryo-EM) structure of the WHV capsid at nanometer resolution and characterization of wCp149 assembly. At this resolution, the T=4 capsid structures of WHV and HBV are practically identical. In contrast to their structural similarity, wCp149 demonstrates enhanced assembly kinetics and stronger dimer-dimer interactions than hCp149: at 23 °C and at 100 mM ionic strength, the pseudocritical concentrations of assembly of wCp149 and hCp149 are 1.8 μM and 43.3 μM, respectively. Transmission electron microscopy reveals that wCp149 assembles into predominantly T=4 capsids with a sizeable population of larger, nonicosahedral structures. Charge detection mass spectrometry indicates that T=3 particles are extremely rare compared to the ∼ 5% observed in hCp149 reactions. Unlike hCp149, wCp149 capsid assembly is favorable over a temperature range of 4 °C to 37 °C; van't Hoff analyses relate the differences in temperature dependence to the high positive values for heat capacity, enthalpy, and entropy of wCp149 assembly. Because the final capsids are so similar, these findings suggest that free wCp149 and hCp149 undergo different structural transitions leading to assembly. The difference in the temperature dependence of wCp149 assembly may be related to the temperature range of its hibernating host.
  
  
  OBJECTIVE
  In this paper, we present a cryo-EM structure of a WHV capsid showing its similarity to HBV. We then observe that the assembly properties of the two homologous proteins are very different. Unlike human HBV, the capsid protein of WHV has evolved to function in a nonhomeostatic environment. These studies yield insight into the interplay between core protein self-assembly and the host environment, which may be particularly relevant to plant viruses and viruses with zoonotic cycles involving insect vectors.
authors.affiliation: Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Kukreja
authors.affiliation: Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Joseph C-Y
authors.initials: JC
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Pierson
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: David Z
authors.initials: DZ
authors.lastname: Keifer
authors.affiliation: Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Selzer
authors.affiliation: Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Zhenning
authors.initials: Z
authors.lastname: Tan
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Bogdan
authors.initials: B
authors.lastname: Dragnea
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana, USA.
authors.forename: Martin F
authors.initials: MF
authors.lastname: Jarrold
authors.affiliation: Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA azlotnic@indiana.edu.
authors.forename: Adam
authors.initials: A
authors.lastname: Zlotnick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020285:Cryoelectron Microscopy; D015613:Hepadnaviridae / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D017919:Hepatitis B Virus, Woodchuck / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D006801:Humans; D013058:Mass Spectrometry; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D013696:Temperature; D014758:Viral Core Proteins / Q000378:metabolism*; D014771:Virion / Q000378:metabolism* / Q000648:ultrastructure; D019065:Virus Assembly / Q000528:radiation effects*
chemical_list: D014758:Viral Core Proteins