Mechanism, structural and functional insights into nidovirus-induced double-membrane vesicles

Abstract

During infection, positive-stranded RNA causes a rearrangement of the host cell membrane, resulting in specialized membrane structure formation aiding viral genome replication. Double-membrane vesicles (DMVs), typical structures produced by virus-induced membrane rearrangements, are platforms for viral replication. Nidoviruses, one of the most complex positive-strand RNA viruses, have the ability to infect not only mammals and a few birds but also invertebrates. Nidoviruses possess a distinctive replication mechanism, wherein their nonstructural proteins (nsps) play a crucial role in DMV biogenesis. With the participation of host factors related to autophagy and lipid synthesis pathways, several viral nsps hijack the membrane rearrangement process of host endoplasmic reticulum (ER), Golgi apparatus, and other organelles to induce DMV formation. An understanding of the mechanisms of DMV formation and its structure and function in the infectious cycle of nidovirus may be essential for the development of new and effective antiviral strategies in the future.

Keywords: DMV; membrane remodeling; nidoviruses; virus replication; virus-cell interaction.

Figure 1

The order Nidovirales genome organization. Schematic diagram of coronavirus, arterivirus, torovirus, ronivirus, and mesonivirus. The 5′ leader sequences are depicted by a small black box; open reading frames are shown by boxes; the proteins encoded by the ORFs are indicated above or below; Spike protein (S), membrane protein (M), envelope protein (E), nucleocapsid protein (N), hemagglutinin-esterase protein (HE), and glycoprotein (GP).

Figure 2

Schematic diagram of nidovirus-induced DMV biogenesis and membrane modifications. The cisternae are formed by the pairing of membranes and the induction of positive and negative curvature at the outer and inner membranes, which ultimately result in the sealing and transformation of the structure into a closed DMV. In nidovirus-infected cells, ER membranes pair to form cisternae. Subsequently, the curve and fission of these cisternae result in the formation of interconnected, independent, or ER-connected DMVs. Infection with nidoviruses also results in the formation of additional virus-induced membrane structures, including paired membranes (PMs), single-membrane vesicles (SMVs), double-membrane spherules (DMSs), zippered ER (Zip-ER), and convoluted membranes (CMs) that are known as highly labyrinthine structures.

Figure 3

Schematic diagram of the mechanism for DMV formation in coronavirus-infected cells. Coronaviruses initiate infection through the process of membrane fusion in endosomes, whereby the virus is released into the host cytoplasm. The released genomic RNA is translated and then cleaved to produce nsp3, nsp4, and nsp6. Nsp3 and nsp4 are hydrolyzed and bound to the host ER. They interact with each other by the luminal loop domains in order to modulate ER membrane curvature and induce membrane-pairing, thereby causing membrane rearrangements. This process might involve nsp6.

Figure 4

Schematic diagram of potential host and viral targets associated with the inhibition of DMV formation, along with methods to reduce the expression of related targets. On the one hand, DMV formation can be effectively hindered by inhibiting host factors associated with DMV biogenesis. On the other hand, disrupting the structural sites of the viral nsps is effective in decreasing the biogenesis of DMV.