A pocket-factor–triggered conformational switch in the hepatitis B virus capsid

Abstract

Viral hepatitis is growing into an epidemic illness, and it is urgent to neutralize the main culprit, hepatitis B virus (HBV), a small-enveloped retrotranscribing DNA virus. An intriguing observation in HB virion morphogenesis is that capsids with immature genomes are rarely enveloped and secreted. This prompted, in 1982, the postulate that a regulated conformation switch in the capsid triggers envelopment. Using solid-state NMR, we identified a stable alternative conformation of the capsid. The structural variations focus on the hydrophobic pocket of the core protein, a hot spot in capsid–envelope interactions. This structural switch is triggered by specific, high-affinity binding of a pocket factor. The conformational change induced by the binding is reminiscent of a maturation signal. This leads us to formulate the “synergistic double interaction” hypothesis, which explains the regulation of capsid envelopment and indicates a concept for therapeutic interference with HBV envelopment.

Amino acid residues at core protein dimer-dimer interface modulate multiple steps of hepatitis B virus replication and HBeAg biogenesis

“…Intriguingly, although Southern blot analysis indicated that rcDNA was synthesized in the cells supporting all the Cp mutant HBV examined (Fig 1A), P25G and T33N mutations excluded the envelopment of rcDNA-containing nucleocapsids. On the contrary, T33G and I105F mutations enabled the envelopment of immature nucleocapsids with single-stranded DNA (S5 Fig) . It was reported recently that the conformation of a hydrophobic pocket at the bottom of spikes on the surface of capsids may be critical for specific interaction with envelop proteins and virion morphogenesis [62]. It is thus possible that these Cp mutations altered the conformation of this pocket and consequentially reduced the efficiency and specificity of nucleocapsid envelopment.…”

Molecular Basis of Antigenic Drift in Serotype O Foot-and-Mouth Disease Viruses (2013–2018) from Southeast Asia

“…In case of rhinoviruses, the canyon regions were shown to contain the binding sites for the cellular receptor [ 47 ]. In hepatitis B virus (HBV), substitutions in the hydrophobic pocket of the core protein resulted in a significant conformational alternation of the capsid [ 48 ]. This residue (VP2 130) also had a very high variability score with four alternate aa residues ( Table 3 A).…”

The Hepatitis B Virus Nucleocapsid—Dynamic Compartment for Infectious Virus Production and New Antiviral Target

“…], can thus accurately reveal where changes happen. Examples include the hinge residues in or changes induced by capsid-binding heterologous molecules such as the detergent Triton X100 [73] yet also therapeutically relevant molecules. Recent technical progress resulted in ever lower sample size requirements (in the submilligram range), and higher magnetic fields in proton resonance frequencies of 1200 MHz in ever higher resolution [153].…”

“…Recent data indicate a more complex situation, with envelopment of empty vs. mature DNA containing capsids having both common and distinct determinants [ 72 ]. Using solid-state nuclear magnetic resonance (ssNMR; see below) we recently identified Triton X-100, used as a detergent during work-up of recombinant Cp capsids, as capable of specifically binding into a hydrophobic pocket in Cp and cause a major conformational shift in the capsid [ 73 ]. As many Cp mutations affecting capsid envelopment also contribute to this pocket, we proposed that occupancy of the pocket by a natural pocket factor, either cellular or viral, is involved in signaling readiness for envelopment.…”

“…Notably, solid-state nuclear magnetic resonance (ssNMR) is gaining increasing interest as high-resolution structural technique because it can be performed under near-physiological conditions, including temperature, and because it can detect conformational alterations at individual protein residues with atomic resolution [ 152 ]. As the characteristic NMR chemical shifts are influenced by the environment comparison with a reference structure of capsids from wt vs. mutant Cp, or similarly of neat capsids vs. capsids with a bound ligand [ 73 ], can thus accurately reveal where changes happen. Examples include the hinge residues in Cp [ 91 ] that distinguish the four quasi-equivalent A, B, C, and D conformers in a T = 4 particle ( Figure 4 C); alterations caused by mutations, e.g., the F97L exchange ( Figure 8 ); or changes induced by capsid-binding heterologous molecules such as the detergent Triton X100 [ 73 ] yet also therapeutically relevant molecules.…”