Evidence that Processing of the Severe Fever with Thrombocytopenia Syndrome Virus Gn/Gc Polyprotein Is Critical for Viral Infectivity and Requires an Internal Gc Signal Peptide.

Teresa Plegge,Martin Spiegel,Stefan Pöhlmann,Heike Hofmann-Winkler,Zheng Xing

doi:10.1371/journal.pone.0166013

Abstract

The severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging, highly pathogenic bunyavirus against which neither antivirals nor vaccines are available. The SFTSV glycoproteins, Gn and Gc, facilitate viral entry into host cells. Gn and Gc are generated from a precursor protein, Gn/Gc, but it is currently unknown how the precursor is converted into the single proteins and whether this process is required for viral infectivity. Employing a rhabdoviral pseudotyping system, we demonstrate that a predicted signal sequence at the N-terminus of Gc is required for Gn/Gc processing and viral infectivity while potential proprotein convertase cleavage sites in Gc are dispensable. Moreover, we show that expression of Gn or Gc alone is not sufficient for host cell entry while particles bearing both proteins are infectious, and we provide evidence that Gn facilitates Golgi transport and virion incorporation of Gc. Collectively, these results suggest that signal peptidase liberates mature Gc from the Gn/Gc precursor and that this process is essential for viral infectivity and thus constitutes a potential target for antiviral intervention.

Highlights

Bunyaviruses constitute the largest RNA virus family and infect a wide range of hosts, including humans, arthropods and plants
For Ebola virus GP (EBOV-GP) and LASV-GPC, the expected C-terminal processing products of 20 kDa and 35 kDa were detected in addition to the precursor proteins (Fig 1A), indicating that these glycoproteins were processed by host cell proteases
Signals corresponding to the molecular weight expected for mature Gc were detected in cells expressing severe fever with thrombocytopenia syndrome virus (SFTSV), Rift Valley fever virus (RVFV) and LACV Gn/Gc proteins (Fig 1A)

Summary

Introduction

Bunyaviruses constitute the largest RNA virus family and infect a wide range of hosts, including humans, arthropods and plants. Several emerging bunyaviruses pose a considerable threat to human health as exemplified by Rift Valley fever virus (RVFV) [1], Crimean Congo hemorrhagic fever virus (CCHFV) [2] and severe fever with thrombocytopenia syndrome virus (SFTSV) [3,4], which can cause severe disease in afflicted patients. SFTSV, a novel member of the phlebovirus genus, emerged in 2007 in Central and Eastern China [5,6]. The virus is transmitted from ticks to humans, with human to human transmission occurring on rare instances [7,8,9], and can induce a severe disease characterized by fever, gastrointestinal symptoms and thrombocytopenia. The case-fatality rate is approximately 10% in China, with the elderly being

Methods

Results

Conclusion