{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,22]],"date-time":"2026-10-22T14:35:05Z","timestamp":1792679705649,"version":"4.5.0"},"reference-count":51,"publisher":"National Academy of Sciences","issue":"14","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2009,4,7]]},"abstract":"<jats:p>The coronavirus spike protein (S) plays a key role in the early steps of viral infection, with the S1 domain responsible for receptor binding and the S2 domain mediating membrane fusion. In some cases, the S protein is proteolytically cleaved at the S1\u2013S2 boundary. In the case of the severe acute respiratory syndrome coronavirus (SARS-CoV), it has been shown that virus entry requires the endosomal protease cathepsin L; however, it was also found that infection of SARS-CoV could be strongly induced by trypsin treatment. Overall, in terms of how cleavage might activate membrane fusion, proteolytic processing of the SARS-CoV S protein remains unclear. Here, we identify a proteolytic cleavage site within the SARS-CoV S2 domain (S2\u2032, R797). Mutation of R797 specifically inhibited trypsin-dependent fusion in both cell\u2013cell fusion and pseudovirion entry assays. We also introduced a furin cleavage site at both the S2\u2032 cleavage site within S2 793-KPTKR-797 (S2\u2032), as well as at the junction of S1 and S2. Introduction of a furin cleavage site at the S2\u2032 position allowed trypsin-independent cell\u2013cell fusion, which was strongly increased by the presence of a second furin cleavage site at the S1\u2013S2 position. Taken together, these data suggest a novel priming mechanism for a viral fusion protein, with a critical proteolytic cleavage event on the SARS-CoV S protein at position 797 (S2\u2032), acting in concert with the S1\u2013S2 cleavage site to mediate membrane fusion and virus infectivity.<\/jats:p>","DOI":"10.1073\/pnas.0809524106","type":"journal-article","created":{"date-parts":[[2009,3,24]],"date-time":"2009-03-24T22:29:06Z","timestamp":1237933746000},"page":"5871-5876","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":967,"title":["Activation of the SARS coronavirus spike protein via sequential proteolytic cleavage at two distinct sites"],"prefix":"10.1073","volume":"106","author":[{"given":"Sandrine","family":"Belouzard","sequence":"first","affiliation":[{"name":"Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Victor C.","family":"Chu","sequence":"additional","affiliation":[{"name":"Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gary R.","family":"Whittaker","sequence":"additional","affiliation":[{"name":"Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[2009,4,7]]},"reference":[{"key":"e_1_3_3_1_2","doi-asserted-by":"publisher","DOI":"10.1080\/10409230802058320"},{"key":"e_1_3_3_2_2","doi-asserted-by":"publisher","DOI":"10.1038\/nsmb.1456"},{"key":"e_1_3_3_3_2","doi-asserted-by":"publisher","DOI":"10.1038\/nrm1076"},{"key":"e_1_3_3_4_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.sbi.2007.08.016"},{"key":"e_1_3_3_5_2","doi-asserted-by":"crossref","first-page":"279","DOI":"10.1002\/3527606769.ch12","volume-title":"Protein\u2013Lipid Interactions","author":"Lai AL","year":"2005","unstructured":"AL Lai, Y Li, LK Tamm Protein\u2013Lipid Interactions, ed LK Tamm (Wiley-VCH, Weinheim, Germany), pp. 279\u2013303 (2005)."},{"key":"e_1_3_3_6_2","first-page":"253","volume-title":"Animal Viruses: Molecular Biology","author":"Klenk HD","year":"2008","unstructured":"HD Klenk, M Matrosovich, J Stech Animal Viruses: Molecular Biology, eds TC Mettenleiter, F Sobrino (Caister Academic, Norfolk, UK), pp. 253\u2013303 (2008)."},{"key":"e_1_3_3_7_2","first-page":"241","volume-title":"Cellular Receptors for Animal Viruses","author":"Klenk HD","year":"1994","unstructured":"HD Klenk, W Garten Cellular Receptors for Animal Viruses, ed E Wimmer (Cold Spring Harbor Press, Cold Spring Harbor, NY), pp. 241\u2013280 (1994)."},{"key":"e_1_3_3_8_2","first-page":"3","volume-title":"Coronaviruses: Molecular and Cellular Biology","author":"Wentworth DE","year":"2007","unstructured":"DE Wentworth, KV Holmes Coronaviruses: Molecular and Cellular Biology, ed V Thiel (Caister Academic, Norfolk, UK), pp. 3\u201331 (2007)."},{"key":"e_1_3_3_9_2","first-page":"157","volume-title":"Nidoviruses","author":"Bosch BJ","year":"2008","unstructured":"BJ Bosch, PJ Rottier Nidoviruses, eds S Perlman, T Gallagher, EJ Snijder (ASM Press, Washington, DC), pp. 157\u2013178 (2008)."},{"key":"e_1_3_3_10_2","doi-asserted-by":"publisher","DOI":"10.1128\/JVI.78.19.10328-10335.2004"},{"key":"e_1_3_3_11_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.bbrc.2003.11.054"},{"key":"e_1_3_3_12_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.bbrc.2004.11.063"},{"key":"e_1_3_3_13_2","doi-asserted-by":"publisher","DOI":"10.1128\/JVI.78.12.6134-6142.2004"},{"key":"e_1_3_3_14_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0306446101"},{"key":"e_1_3_3_15_2","doi-asserted-by":"publisher","DOI":"10.1128\/JVI.78.11.5642-5650.2004"},{"key":"e_1_3_3_16_2","doi-asserted-by":"publisher","DOI":"10.1128\/JVI.01697-07"},{"key":"e_1_3_3_17_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0503203102"},{"key":"e_1_3_3_18_2","first-page":"3198","article-title":"SARS coronavirus, but not human coronavirus NL63, utilizes cathepsin L to infect ACE2-expressing cells","volume":"10","author":"Huang IC","year":"2005","unstructured":"IC Huang, et al., SARS coronavirus, but not human coronavirus NL63, utilizes cathepsin L to infect ACE2-expressing cells. 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