Nora Gibes, Biochemistry fourth year student in the Zlotnick lab, won a "Best Oral Presentation" award at the 2022 International HBV Meeting.
Title: A mature DHBV core encapsidates a spool of dsDNA
Abstract: Duck Hepatitis B Virus (DHBV) and Hepatitis B Virus are closely related hepadnaviruses. For both viruses, the immature core is filled with viral RNA which is reverse transcribed to circular dsDNA within the viral capsid to yield the mature core. We purified DHBV nucleocapsids from LMH cells to probe the organization of the dsDNA and the effect of genome packaging on the capsid structure. We subjected the capsids to cryo-EM reconstruction and observed three particle sizes: T = 4, T = 3, and small, potentially asymmetric capsids. We observed folded extended regions in the spike domain of the dimeric capsid protein. These extensions have been previously observed in DHBV capsid spikes but appear to fold very slowly in-vitro—our results would indicate that the extension domains are able to fully fold in a eukaryotic cell before capsid envelopment and egress. Additionally, we see that the four-helix bundle at the dimer interface has a left-handed supercoil, unlike in the human HBV. We performed focused, asymmetric 3D-classification on the T = 4 particles and observed the viral dsDNA forming a spool with an axis extending from fivefold to fivefold. A spooled genome is frequently observed in bacteriophages and has now been seen in hepadnaviridae. We hypothesize that the spool forms inside the capsid during the reverse transcription process and may contribute to the meta-stable nature of the mature virion.