The spike (S) protein of SARS coronavirus (SARS-CoV) has been known to recognize and bind to host receptors, whose conformational changes then facilitates fusion between the viral envelope and host cell membrane, leading to viral entry into target cells. However, other functions of SARS-CoV S protein such as proteolytic cleavage and its implications to viral infection are incompletely understood. In this study, we demonstrated that the infection of SARS-CoV and a pseudovirus bearing the S protein of SARS-CoV was inhibited by a protease inhibitor Ben-HCl. Also, the protease Factor Xa, a target of Ben-HCl abundantly expressed in infected cells, was able to cleave the recombinant and pseudoviral S protein into S1 and S2 subunits, and the cleavage was inhibited by Ben-HCl. Furthermore, this cleavage correlated with the infectivity of the pseudovirus. Taken together, our study suggests a plausible mechanism by which SARS-CoV cleaves its S protein to facilitate viral infection.
Keywords
SARS-CoV; Spike protein; Protease Factor Xa; Protease inhibitor; Cleavage of S proteinSevere acute respiratory syndrome (SARS) is a novel life-threatening infectious disease caused by SARS-coronavirus (SARS-CoV) [1]. Viral spike (S) protein is a multifunctional protein that plays pivotal roles in the biology and pathogenesis of SARS-CoV. The N-terminal region of the S protein has been demonstrated to mediate viral infection, by binding through the receptor-binding domain (RBD) to a cellular receptor angiotensin-converting enzyme 2 (ACE2) [2], and subsequently inducing virus-cell membrane fusion, which involves two domains in the C-terminal region of the S protein named heptad repeat (HR) 1 and 2 [3]. However, other functions of the S protein that are important in viral infection have not yet been defined. * Corresponding author: Fax: +852 2855 1241; E-mail address: bzheng@hkucc.hku.hk. (B.J. Zheng). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. In most other members of the coronavirus family, such as human coronavirus HCoV-OC43 and bovine coronaviruses BCoV, the S protein may be post-translationally cleaved into two fragments, S1 (receptor binding domain) and S2 (membrane fusion domain) [4,5]. Studies in other coronaviruses have further elucidated that conformational changes of the S protein can be induced at 37 °C and pH 8.0, accompanied by the cleavage of S1 and S2, which triggers virus-cell membrane fusion [6,7]. As a new member of the coronavirus family, SARS-CoV shares with other coronaviruses some similarity and common features in the amino acid sequences of the S protein [8]. It...