Structural and Functional Diversity of Nairovirus-Encoded Nucleoproteins

Abstract

The nairoviruses include assorted tick-borne bunyaviruses that are emerging as causative agents of infectious diseases among humans and animals. As negative-sense single-stranded RNA (؊ssRNA) viruses, nairoviruses encode nucleoprotein (NP) that encapsidates the genomic RNA and further forms ribonucleoprotein (RNP) complex with viral RNA-dependent RNA polymerase (RdRp). We previously revealed that the monomeric NP encoded by Crimean-Congo hemorrhagic fever virus (CCHFV) presents a racket-shaped structure and shows unusual DNA-specific endonuclease activity. To examine the structural and biological variation of nairovirus-encoded NPs, here, we systematically solved the crystal structures of NPs encoded by various nairoviruses, including Hazara virus (HAZV), Kupe virus (KUPV), and Erve virus (ERVEV). Combined with biochemical analysis, our results generate a clearer picture to aid in the understanding of the functional diversity of nairovirus-encoded NPs and the formation of nairovirus RNPs. IMPORTANCENairoviruses comprise several tick-borne bunyaviruses that are emerging as causative agents of infectious diseases among humans and animals; however, little is known of the nairovirus genome assembly and transcription mechanisms. Based on the previous study of CCHFV NP reported by different research groups, we systematically investigate here the structural and functional diversity among three different nairoviruses. This work provides important information on nairovirus nucleoprotein function and the formation of RNPs. Bunyaviridae is the largest negative-sense, single-stranded (ϪssRNA) virus family and contains various pathogens that cause severe infectious diseases in humans, other animals, and plants (1). Over 300 members of the Bunyaviridae family are currently classified into five distinct genera, i.e., Orthobunyavirus, Hantavirus, Nairovirus, Phlebovirus, and Tospovirus (1). Bunyaviruses are characterized by their trisegmented negative-sense genome, in which the large (L) segment encodes RNA-dependent RNA polymerase (RdRp), the medium (M) segment encodes surface glycoproteins, and the small (S) segment encodes nucleocapsid (NP) protein (1). As in other ϪssRNA viruses, the genomic RNA of bunyaviruses does not exist as a naked RNA but must be encapsidated by viral NP to form a high-order NP-RNA complex, which further constructs a ribonucleoprotein (RNP) complex with viral RdRp (2, 3).The Nairovirus genus comprises a number of pathogens that cause infectious diseases in humans and livestock. Nairoviruses are transmitted by ticks, which distinguishes them from other members of the Bunyaviridae family (4). Based on antibody crossreactivities, nairoviruses are classified into seven serogroups (see Table S1 in the supplemental material) (5). CCHFV, which belongs to the CCHF serogroup, is the most notable pathogen: it causes CCHF in humans, with high mortality, and occurs spontaneously in more than 30 countries in Asia, the Middle East, southeastern Europe, and Africa (6). The high pathogenicity of CCHFV has led...

Structural Insight into Nucleoprotein Conformation Change Chaperoned by VP35 Peptide in Marburg Virus

“…The first group includes most of the nonsegmented or segmented ϪssRNA viruses, such as BDV (17) from the Bornaviridae family, VSV (18,19,42) and rabies virus (43) from the Rhabdoviridae family, RSV (20) from the Paramyxoviridae family, influenza virus (44) from the Orthomyxoviridae family, Rift Valley fever virus (RVFV) (45) from the Phenuiviridae family, Sin Nombre orthohantavirus (15) from the Hantaviridae family, and Bunyamwera virus (BUNV) (46) from the Peribunyaviridae family. The structural feature of the second group was discovered after 2010; this group includes LAFV (10,11) and Junin virus (47) in the Arenaviridae family and CCHFV (12) and Hazara orthonairovirus (48,49) in the Nairoviridae family. In this group, NPs do not exhibit as the typical divided two lobes; however, the positivecharged RNA binding groove is located at the center of one compact domain, which adopts an interesting gating mechanism for virus genome encapsidation; moreover, these NPs also show unanticipated enzymatic activities.…”

Crystal Structure of the Core Region of Hantavirus Nucleocapsid Protein Reveals the Mechanism for Ribonucleoprotein Complex Formation

“…The RNP either further serves as an active template for RNA synthesis or is packaged into the virion (8)(9)(10). Since 2010, a series of structural studies, including studies on the structures of NPs encoded by phleboviruses (Rift Valley fever virus [RVFV] [11][12][13] and severe fever with thrombocytopenia syndrome virus [SFTSV] [14]), nairovirus (CrimeanCongo hemorrhagic fever virus [CCHFV]) (6,15,16), and orthobunyaviruses (Bunyamwera virus [BUNV], etc.) (17)(18)(19)(20)(21), has advanced the understanding of the structures and functions of bunyavirus NPs.…”

Sin Nombre hantavirus nucleocapsid protein exhibits a metal-dependent DNA-specific endonucleolytic activity

“…In the family of Bunyaviridae, nucleases were detected in RdRP of La Crosse virus (genus orthobunyavirus) (Reguera et al, 2010), Crimean Congo hemorrhagic fever virus (genus nairovirus) (Devignot et al, 2015) and Andes virus (genus hantavirus) (Heinemann et al, 2013). Nuclease activity in the nucleocapsid protein was only shown in the genus nairovirus so far (Guo et al, 2012;Wang et al, 2015). In all these examples the nuclease activity was predicted and confirmed upon solution of the corresponding crystal structures.…”

“…In this work, we addressed the question whether the hantavirus N protein has a nucleic acid-degrading function as previously reported for the N protein of several nairoviruses, a genus which also belongs to the Bunyaviridae family (Guo et al, 2012;Wang et al, 2015). Sin Nombre hantavirus (strain Convict Creek 107) nucleoprotein open reading frame (ORF) was cloned into the glutathione-S-transferase (GST) expression vector pGEX-6P-1, thus providing the full-length N protein with an N-terminal GST-tag.…”

“…It was demonstrated for viruses that belong to the families of Orthomyxo- (Dias et al, 2009;Yuan et al, 2009), Arena- (Hastie et al, 2011a;Jiang et al, 2013;Martinez-Sobrido et al, 2009;Morin et al, 2010;Qi et al, 2010;Wallat et al, 2014;West et al, 2014) and Bunyaviridae (Devignot et al, 2015;Guo et al, 2012;Heinemann et al, 2013;Reguera et al, 2010;Wang et al, 2015). In the family of Bunyaviridae, nucleases were detected in RdRP of La Crosse virus (genus orthobunyavirus) (Reguera et al, 2010), Crimean Congo hemorrhagic fever virus (genus nairovirus) (Devignot et al, 2015) and Andes virus (genus hantavirus) (Heinemann et al, 2013).…”