The Role of Hepatitis-B Virus Capsid Phosphorylation In Genome Packaging

Friday, November 08, 2013 — Poster Session IV
2:00 p.m. – 4:00 p.m.	FAES Academic Center (Upper-Level Terrace)	NIAMS	STRUCTBIO-18

Authors

G. Tolun
N. Cheng
B.J. Heymann
P.T. Wingfield
L. Ludgate
J Hu
A.C. Steven

Abstract

Of the 350 million persons chronically infected with hepatitis B virus, up to 25% will eventually have a fatal outcome. One of the crucial steps in HBV life cycle is its genome packaging whose mechanistic details remain unknown. HBV packs a pregenomic RNA (pgRNA) into its capsid, and the C-terminal domain (CTD) of the capsid protein (Cp) is known to be involved in this process. We aim to understand the function of phosphorylation of three serine residues in CTD. Capsid samples were prepared by expressing Cp constructs, wild-type (wt) and a mutant form with three phosphorylation-target serines in the CTD mutated to alanines (3A), in HEK293T cells; and by co-expressing the wt construct together with the viral polymerase and pgRNA in HepG-2 cells (wt-2). Cryo EM reconstructions show that the 3A mutant packages ~3 fold more nucleic acids than wt. Contrarily, 3A mutation was reported to suppress pgRNA encapsidation. As we identified the nucleic acids packaged into non-phosphorylated capsids mostly being tRNAs, it is the nonspecific packaging that increases in the absence of phosphorylation. Hence, we propose that the mechanistic function of CTD phosphorylation as the differentiation of pgRNA of HBV from non-specific RNAs, such as host tRNAs, during packaging.