tetano
Editor, Senior Moderator
Host cell entry of Middle East respiratory syndrome coronavirus after two-step, furin-mediated activation of the spike protein
Jean Kaoru Millet and
Gary R. Whittaker1
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853
Edited by Ari Helenius, ETH Zurich, Zurich, Switzerland, and approved September 15, 2014 (received for review April 18, 2014)
Significance
The emergence of Middle East respiratory syndrome coronavirus (MERS-CoV), a deadly human coronavirus, has triggered considerable interest in the biomedical community. Similar to other enveloped viruses, coronaviruses access host cells by membrane fusion, a process mediated by specific fusion or ?spike? proteins on the virion, often activated by cellular proteases. We have identified unique features of the MERS-CoV spike (S) protein cleavage activation. Our findings suggest that S can be activated by furin, a broadly expressed protease, by a two-step cleavage mechanism, occurring at distinct sites, with cleavage events temporally separated. Such furin-mediated activation is unusual in that it occurs in part during virus entry. Our findings may explain the polytropic nature, pathogenicity, and life cycle of this zoonotic coronavirus.
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly identified betacoronavirus causing high morbidity and mortality in humans. The coronavirus spike (S) protein is the main determinant of viral entry, and although it was previously shown that MERS-CoV S can be activated by various proteases, the details of the mechanisms of proteolytic activation of fusion are still incompletely characterized. Here, we have uncovered distinctive characteristics of MERS-CoV S. We identify, by bioinformatics and peptide cleavage assays, two cleavage sites for furin, a ubiquitously expressed protease, which are located at the S1/S2 interface and at the S2′ position of the S protein. We show that although the S1/S2 site is proteolytically processed by furin during protein biosynthesis, the S2′ site is cleaved upon viral entry. MERS-CoV pseudovirion infection was shown to be enhanced by elevated levels of furin expression, and entry could be decreased by furin siRNA silencing. Enhanced furin activity appeared to partially override the low pH-dependent nature of MERS-CoV entry. Inhibition of furin activity was shown to decrease MERS-CoV S-mediated entry, as well as infection by the virus. Overall, we show that MERS-CoV has evolved an unusual two-step furin activation for fusion, suggestive of a role during the process of emergence into the human population. The ability of MERS-CoV to use furin in this manner, along with other proteases, may explain the polytropic nature of the virus.
http://www.pnas.org/content/early/2014/10/02/1407087111.abstract
Jean Kaoru Millet and
Gary R. Whittaker1
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853
Edited by Ari Helenius, ETH Zurich, Zurich, Switzerland, and approved September 15, 2014 (received for review April 18, 2014)
Significance
The emergence of Middle East respiratory syndrome coronavirus (MERS-CoV), a deadly human coronavirus, has triggered considerable interest in the biomedical community. Similar to other enveloped viruses, coronaviruses access host cells by membrane fusion, a process mediated by specific fusion or ?spike? proteins on the virion, often activated by cellular proteases. We have identified unique features of the MERS-CoV spike (S) protein cleavage activation. Our findings suggest that S can be activated by furin, a broadly expressed protease, by a two-step cleavage mechanism, occurring at distinct sites, with cleavage events temporally separated. Such furin-mediated activation is unusual in that it occurs in part during virus entry. Our findings may explain the polytropic nature, pathogenicity, and life cycle of this zoonotic coronavirus.
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly identified betacoronavirus causing high morbidity and mortality in humans. The coronavirus spike (S) protein is the main determinant of viral entry, and although it was previously shown that MERS-CoV S can be activated by various proteases, the details of the mechanisms of proteolytic activation of fusion are still incompletely characterized. Here, we have uncovered distinctive characteristics of MERS-CoV S. We identify, by bioinformatics and peptide cleavage assays, two cleavage sites for furin, a ubiquitously expressed protease, which are located at the S1/S2 interface and at the S2′ position of the S protein. We show that although the S1/S2 site is proteolytically processed by furin during protein biosynthesis, the S2′ site is cleaved upon viral entry. MERS-CoV pseudovirion infection was shown to be enhanced by elevated levels of furin expression, and entry could be decreased by furin siRNA silencing. Enhanced furin activity appeared to partially override the low pH-dependent nature of MERS-CoV entry. Inhibition of furin activity was shown to decrease MERS-CoV S-mediated entry, as well as infection by the virus. Overall, we show that MERS-CoV has evolved an unusual two-step furin activation for fusion, suggestive of a role during the process of emergence into the human population. The ability of MERS-CoV to use furin in this manner, along with other proteases, may explain the polytropic nature of the virus.
http://www.pnas.org/content/early/2014/10/02/1407087111.abstract