Birnaviral Hijacking of Endosomal Membranes

FLAVIA A. ZANETTI; IGNACIO FERNANDEZ; EDUARD BAQUERO; PABLO GUARDADO-CALVO; SARAH DUBOIS; ETIENNE MOREL; VICTORIA ALFONSO; MILTON O. AGUILERA; MARÍA E. CELAYES; LUIS M. POLO; LAILA SUHAIMAN; VANESA V. GALASSI; M. VANINA CHIARPOTTI; CAROLINA ALLENDE; JAVIER M. RODRÍGUEZ; JOSÉ R. CASTÓN; DIEGO LIJAVETZKY; OSCAR TABOGA; MARÍA I. COLOMBO; DEL PÓPOLO, MARIO; FÉLIX A. REY; LAURA R. DELGUI

eLife

eLife Sciences Publications Ltd.

Lugar: Cambridge; Año: 2024

2050-084X

Birnaviruses form a distinct class of double-stranded RNA (dsRNA) viruses characterized by the absence of a transcription-competent inner core particle, a hallmark of all other dsRNA viruses. We have previously shown that the early endosomes (EE) of cells infected with the infectious bursal disease virus (IBDV) - a prototypical birnavirus and an important avian  pathogen - constitute a platform for viral replication. Here, we study the mechanism of birnaviral hijacking of EE membranes for this process. Using biophysical approaches in cell-free in vitro systems, we demonstrate  that the viral protein 3 (VP3) specifically binds to phosphatidylinositol-3-phosphate (PI3P) present in EE membranes.  Furthermore, we identify the domain of VP3 involved in PI3P-binding,  termed “Patch 2” (P2), and we establish the contribution of each of the four positively charged residues composing P2, with a critical role for the arginine at position 200 (R200) of VP3, conserved among all known  virnaviruses. Using a reverse genetic system for IBDV, we show that  mutating R200 abolishes viral replication. Finally, our molecular simulations results allow us to propose a two-stage modular mechanism for VP3 association with EE. In the first step, the carboxy-terminal region of VP3 adsorbs to the membrane via non-specific electrostatic interactions. Then, in the second stage, the VP3 core seals the membrane engagement by specifically binding PI3P through its P2 domain, additionally promoting PI3P accumulation.