Measles virus fusion: role of the cysteine-rich region of the fusion glycoprotein

Virulent and moderately virulent strains of Newcastle disease virus (NDV), representing avian paramyxovirus serotype 1 (APMV-1), cause respiratory and neurological disease in chickens and other species of birds. In contrast, APMV-2 is avirulent in chickens. We investigated the role of the fusion (F) and hemagglutininneuraminidase (HN) envelope glycoproteins in these contrasting phenotypes by designing chimeric viruses in which the F and HN glycoproteins or their ectodomains were exchanged individually or together between the moderately virulent, neurotropic NDV strain Beaudette C (BC) and the avirulent APMV-2 strain Yucaipa. When we attempted to exchange the complete F and HN glycoproteins individually and together between the two viruses, the only construct that could be recovered was recombinant APMV-2 strain Yucaipa (rAPMV-2), containing the NDV F glycoprotein in place of its own. This substitution of NDV F into APMV-2 was sufficient to confer the neurotropic, neuroinvasive, and neurovirulent phenotypes, in spite of all being at reduced levels compared to what was seen for NDV-BC. When the ectodomains of F and HN were exchanged individually and together, two constructs could be recovered: NDV, containing both the F and HN ectodomains of APMV-2; and APMV-2, containing both ectodomains of NDV. This supported the idea that homologous cytoplasmic tails and matched F and HN ectodomains are important for virus replication. Analysis of these viruses for replication in vitro, syncytium formation, mean embryo death time, intracerebral pathogenicity index, and replication and tropism in 1-day-old chicks and 2-week-old chickens showed that the two contrasting phenotypes of NDV and APMV-2 could largely be transferred between the two backbones by transfer of homotypic F and HN ectodomains. Further analysis provided evidence that the homologous stalk domain of NDV HN is essential for virus replication, while the globular head domain of NDV HN could be replaced with that of APMV-2 with only a minimal attenuating effect. These results demonstrate that the F and HN ectodomains together determine the cell fusion, tropism, and virulence phenotypes of NDV and APMV-2 and that the regions of HN that are critical to replication and the species-specific phenotypes include the cytoplasmic tail and stalk domain but not the globular head domain.

Section: Discussionsupporting

confidence: 90%

Roles of the Fusion and Hemagglutinin-Neuraminidase Proteins in Replication, Tropism, and Pathogenicity of Avian Paramyxoviruses

Kim

Subbiah

Samuel

et al. 2011

“…Fusion protein chimeric constructs have also further elucidated the role of the fusion protein in regulating membrane fusion. A study showed that switching an ϳ45-amino-acid residue region in canine distemper virus (CDV) F to that of a homologous MeV F region resulted in fusion when triggered by MeV H (34). In a similar study, the substitution of a different region, a central pocket, from MeV F to CDV F also induced fusion when triggered by MeV H (35).…”

mentioning

confidence: 99%

Nipah and Hendra Virus Glycoproteins Induce Comparable Homologous but Distinct Heterologous Fusion Phenotypes

Bradel-Tretheway

Zamora

Stone

et al. 2019

Nipah and Hendra viruses (NiV and HeV) exhibit high lethality in humans and are biosafety level 4 (BSL-4) paramyxoviruses in the growing genus Henipavirus. The attachment (G) and fusion (F) envelope glycoproteins are both required for viral entry into cells and for cell-cell fusion, which is pathognomonic of henipaviral infections. Here, we compared the fusogenic capacities between homologous and heterologous pairs of NiV and HeV glycoproteins. Importantly, to accurately measure their fusogenic capacities, as these depend on glycoprotein cell surface expression (CSE) levels, we inserted identical extracellular tags to both fusion (FLAG tags) or both attachment (hemagglutinin [HA] tags) glycoproteins. Importantly, these tags were placed in extracellular sites where they did not affect glycoprotein expression or function. NiV and HeV glycoproteins induced comparable levels of homologous HEK293T cell-cell fusion. Surprisingly, however, while the heterologous NiV F/HeV G (NF/HG) combination yielded a hypofusogenic phenotype, the heterologous HeV F/NiV G (HF/NG) combination yielded a hyperfusogenic phenotype. Pseudotyped viral entry levels primarily corroborated the fusogenic phenotypes of the glycoprotein pairs analyzed. Furthermore, we constructed G and F chimeras that allowed us to map the overall regions in G and F that contributed to these hyperfusogenic or hypofusogenic phenotypes. Importantly, the fusogenic phenotypes of the glycoprotein combinations negatively correlated with the avidities of F-G interactions, supporting the F/G dissociation model of henipavirus-induced membrane fusion, even in the context of heterologous glycoprotein pairs. IMPORTANCE The NiV and HeV henipaviruses are BSL-4 pathogens transmitted from bats. NiV and HeV often lead to human death and animal diseases. The formation of multinucleated cells (syncytia) is a hallmark of henipaviral infections and is caused by fusion of cells coordinated by interactions of the viral attachment (G) and fusion (F) glycoproteins. We found via various assays that viral entry and syncytium formation depend on the viral origin of the glycoproteins, with HeV F and NiV G promoting higher membrane fusion levels than their counterparts. This is important knowledge, since both viruses use the same bat vector species and potential coinfections of these or subsequent hosts may alter the outcome of disease.

“…A number of previous studies have demonstrated that the cell fusion induced by paramyxovirus glycoproteins requires expression of both glycoproteins (3,5,7,13,21,26,32). Furthermore, the requirement for the HN protein is generally restricted to HN proteins from the same species of virus (2,3,7,11,15,34). It has been suggested that a type-specific interaction occurs between F and HN proteins and is involved in fusion activity (7,12).…”

mentioning

confidence: 99%

Functional interaction of paramyxovirus glycoproteins: identification of a domain in Sendai virus HN which promotes cell fusion

Tanabayashi

Compans

1996

137

The cell fusion activity of most paramyxoviruses requires coexpression of a fusion protein (F) and a hemagglutinin-neuraminidase protein (HN) which are derived from the same virus type. To define the domain of the HN protein which interacts with the F protein in a type-specific manner, a series of chimeric HN proteins between two different paramyxoviruses, Sendai virus (SN) and human parainfluenza virus type 3 (PI3), was constructed and coexpressed with the SN-F protein by using the vaccinia virus T7 RNA polymerase transientexpression system. Quantitative assays were used to evaluate cell surface expression as well as fusion-promoting activities of the chimeric HN molecules. A chimeric HN protein [SN(140)] containing 140 N-terminal amino acids derived from SN-HN and the remainder (432 amino acids) derived from PI3-HN was found to promote cell fusion with the SN-F protein. In contrast, a second chimeric HN with 137 amino acids from SN-HN at the N terminus could not promote fusion with SN-F, even though the protein was expressed on the cell surface. A construct in which the PI3-HN cytoplasmic tail and transmembrane domain were substituted for those of SN in the SN(140) chimera still maintained the ability to promote cell fusion. These results indicate that a region including only 82 amino acids in the extracellular domain, adjacent to the transmembrane domain of the SN-HN protein, is important for interaction with the SN-F protein and promotion of cell fusion.