title: Hepatitis B Virus Capsids Have Diverse Structural Responses to Small-Molecule Ligands Bound to the Heteroaryldihydropyrimidine Pocket.
abstract: Though the hepatitis B virus (HBV) core protein is an important participant in many aspects of the viral life cycle, its best-characterized activity is self-assembly into 240-monomer capsids. Small molecules that target core protein (core protein allosteric modulators [CpAMs]) represent a promising antiviral strategy. To better understand the structural basis of the CpAM mechanism, we determined the crystal structure of the HBV capsid in complex with HAP18. HAP18 accelerates assembly, increases protein-protein association more than 100-fold, and induces assembly of nonicosahedral macrostructures. In a preformed capsid, HAP18 is found at quasiequivalent subunit-subunit interfaces. In a detailed comparison to the two other extant CpAM structures, we find that the HAP18-capsid structure presents a paradox. Whereas the two other structures expanded the capsid diameter by up to 10 Å, HAP18 caused only minor changes in quaternary structure and actually decreased the capsid diameter by ∼3 Å. These results indicate that CpAMs do not have a single allosteric effect on capsid structure. We suggest that HBV capsids present an ensemble of states that can be trapped by CpAMs, indicating a more complex basis for antiviral drug design.
  
  
  OBJECTIVE
  Hepatitis B virus core protein has multiple roles in the viral life cycle-assembly, compartment for reverse transcription, intracellular trafficking, and nuclear functions-making it an attractive antiviral target. Core protein allosteric modulators (CpAMs) are an experimental class of antivirals that bind core protein. The most recognized CpAM activity is that they accelerate core protein assembly and strengthen interactions between subunits. In this study, we observe that the CpAM-binding pocket has multiple conformations. We compare structures of capsids cocrystallized with different CpAMs and find that they also affect quaternary structure in different ways. These results suggest that the capsid "breathes" and is trapped in different states by the drug and crystallization. Understanding that the capsid is a moving target will aid drug design and improve our understanding of HBV interaction with its environment.
authors: Molecular and Cellular Biochemistry Department, Indiana University, Bloomington, Indiana, USA.
authors: Balasubramanian
authors: B
authors: Venkatakrishnan
authors: Assembly Biosciences, Bloomington, Indiana, USA, and San Francisco, California, USA.
authors: Sarah P
authors: SP
authors: Katen
authors: Molecular and Cellular Biochemistry Department, Indiana University, Bloomington, Indiana, USA.|Assembly Biosciences, Bloomington, Indiana, USA, and San Francisco, California, USA.
authors: Samson
authors: S
authors: Francis
authors: Department of Chemistry and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California, USA.|Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, Georgia, USA.
authors: Srinivas
authors: S
authors: Chirapu
authors: Department of Chemistry and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California, USA.|Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, Georgia, USA.
authors: M G
authors: MG
authors: Finn
authors: Molecular and Cellular Biochemistry Department, Indiana University, Bloomington, Indiana, USA azlotnic@indiana.edu.
authors: Adam
authors: A
authors: Zlotnick
mesh_terms: D000495:Allosteric Site; D000998:Antiviral Agents / Q000737:chemistry; D002213:Capsid / Q000737:chemistry* / Q000378:metabolism; D036022:Capsid Proteins / Q000737:chemistry* / Q000378:metabolism; D003461:Crystallography; D006512:Hepatitis B Core Antigens / Q000737:chemistry / Q000378:metabolism; D006515:Hepatitis B virus / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D011743:Pyrimidines / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014758:Viral Core Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D036022:Capsid Proteins; D006512:Hepatitis B Core Antigens; D011743:Pyrimidines; D011994:Recombinant Proteins; D014758:Viral Core Proteins