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Published on: January 9, 2019
Clade C MERS-CoV camel strains vary in protease utilization during viral entry
Helena Winstone1,2, Helen Stillwell1,2, Tiffany Tan3
1Department of Microbiology, University of Pennsylvania.
Abstract:
MERS-CoV is a lethal pathogen with pandemic potential. Clade A and B MERS-CoV viruses have caused outbreaks in the Middle East since 2012 when they initially spilled over from camels to humans. Clade C viruses, however, are only found in camels across Africa and the spillover potential of these viruses seems to be lower than for clade A/B strains but remains to be fully understood. Here, we report that clade C spikes are less well-cleaved at the S1/S2 boundary than clade A or B viral spikes and that most clade C spikes induce reduced syncytium formation. Additionally, we demonstrate that several East African clade C strains are less able to utilize the TMPRSS2-mediated pathway for viral entry in both cell lines and primary nasal epithelial cultures. We map the molecular basis of this reduced TMPRSS2 usage to the N-terminal domain (NTD) and subdomain 2 (SD2) of East African clade C MERS-CoV. We suggest that reduced usage of the TMPRSS2-mediated entry pathway may underlie the reduced replication of East African clade C strains in humans, while the reduced replication of West African strains remains to be further investigated. Overall, we suggest that altered protease usage may contribute to differential tropism of East African clade C strains and indicate geographically distinct selection pressures on spike between MERS-CoV strains circulating in camels.
Insights
Clade C MERS-CoV spikes show reduced cleavage and syncytium formation. This may explain lower human replication of these camel viruses, indicating distinct selection pressures.
Area of Science:
- Virology
- Molecular Biology
- Epidemiology
Background:
- Middle East Respiratory Syndrome Coronavirus (MERS-CoV) poses a pandemic threat.
- Clade A and B MERS-CoV strains caused human outbreaks originating from camels.
- Clade C MERS-CoV strains circulate in African camels with less understood spillover potential.
Purpose of the Study:
- Investigate the molecular and cellular basis for potential differences in MERS-CoV spillover.
- Compare the viral entry mechanisms of Clade C MERS-CoV with Clade A and B strains.
- Identify genetic determinants of MERS-CoV tropism and replication.
Main Methods:
- Analyzed MERS-CoV spike protein cleavage at the S1/S2 boundary.
- Assessed syncytium formation induced by different MERS-CoV clades.
- Evaluated viral entry via the TMPRSS2-mediated pathway in cell lines and primary cultures.
- Mapped the molecular regions responsible for TMPRSS2 usage.
Main Results:
- Clade C MERS-CoV spikes exhibited less efficient cleavage at the S1/S2 boundary compared to Clade A/B.
- Most Clade C spikes induced reduced syncytium formation.
- East African Clade C strains showed impaired utilization of the TMPRSS2 entry pathway.
- Reduced TMPRSS2 usage was mapped to the N-terminal domain (NTD) and subdomain 2 (SD2) of Clade C spikes.
Conclusions:
- Reduced spike cleavage and syncytium formation in Clade C MERS-CoV may contribute to lower human replication.
- Impaired TMPRSS2-mediated entry is a key factor in the differential tropism of East African Clade C strains.
- Geographically distinct selection pressures on the MERS-CoV spike protein likely exist between African and Middle Eastern strains.
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