Oropouche virus glycoprotein topology and cellular requirements for virus-like particle assembly

Abstract

Oropouche virus (OROV; Genus: Orthobunyavirus) is the etiological agent of Oropouche fever, a debilitating febrile illness common in South America. We used recombinant expression of the OROV M polyprotein, that encodes the surface glycoproteins Gn and Gc plus the non-structural protein NSm, to probe the cellular determinants for OROV assembly and budding. Gn and Gc self-assemble and are secreted independently of NSm. Mature OROV Gn has two predicted transmembrane domains that are crucial for glycoprotein translocation to the Golgi complex and glycoprotein secretion and, unlike related orthobunyaviruses, both transmembrane domains are retained during Gn maturation. Disruption of Golgi function using the drugs brefeldin A and monensin inhibit glycoprotein secretion. Infection studies have previously shown that the cellular Endosomal Sorting Complexes Required for Transport (ESCRT) machinery is recruited to Golgi membranes during OROV assembly and that ESCRT activity is required for virus secretion. A dominant negative form of the ESCRT-associated ATPase VPS4 significantly reduces recombinant OROV glycoprotein secretion and blocks virus release from infected cells, and VPS4 partly co-localizes with OROV glycoproteins and membranes co-stained with Golgi markers. Furthermore, immunoprecipitation and fluorescence microscopy experiments demonstrate that OROV glycoproteins interact with the ESCRT-III component CHMP6, with overexpression of a dominant negative form of CHMP6 significantly reducing OROV glycoprotein secretion. Taken together, our data highlights differences in M polyprotein processing across orthobunyaviruses, that Golgi and ESCRT function are required for glycoprotein secretion, and identifies CHMP6 as an ESCRT-III component that interacts with OROV glycoproteins. ImportanceOropouche virus causes Oropouche fever, a debilitating illness common in South America that is characterised by high fever, headache, myalgia and vomiting. The tripartite genome of this zoonotic virus is capable of reassortment and there have been multiple epidemics of Oropouche fever in South America over the last 50 years, making Oropouche virus infection a significant threat to public health. However, the molecular characteristics of this arbovirus are poorly understood. We developed a recombinant protein expression system to investigate the cellular determinants of OROV glycoprotein maturation and secretion. We show that the proteolytic processing of the M polypeptide, which encodes the surface glycoproteins (Gn and Gc) plus a non-structural protein (NSm), differs between OROV and its close relative Bunyamwera virus. Furthermore, we demonstrate that OROV M glycoprotein secretion requires the cellular ESCRT membrane-remodelling machinery and identify that the OROV glycoproteins interact with the ESCRT protein CHMP6.