sGP Serves as a Structural Protein in Ebola Virus Infection

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Abstract
Background. sGP, which is perceived as nonstructural, secretory glycoprotein, shares 295 amino acids at its N-terminal with GP1,2, which include the specific residue necessary to interact with GP2. In the present study, we tested whether the sGP protein of Zaire ebolavirus (ZEBOV) could substitute for GP1 and form a complex with GP2, thus serving as a structural protein. Methods. We expressed ZEBOV GP1,2, VP40, and NP proteins, together with sGP protein, from expression plasmids and examined the resultant virus-like particles by using Western blot. Cells expressing GP2 in combination with either GP1 or sGP were analyzed by using flow cytometry with the KZ52 antibody, which recognizes a GP1,2 conformational epitope. A VSV pseudotype, VSVΔG*, which expresses a GFP reporter gene instead of the G protein, was used to produce pseudotyped viruses encoding sGP and variants of GP to test the contribution of sGP to infectivity. Results. Western blot and flow cytometric analyses suggested the existence of a covalently linked sGP-GP2 molecule. VSVΔG*(sGP + GP2) and VSVΔG*(GP1,2) infected Vero E6 cells and were neutralized by the KZ52 antibody. Overexpression of sGP reduced the titer of VSVΔG*(GP1,2). Conclusions. ZEBOV sGP can substitute for GP1, forming a sGP-GP2 complex and conferring infectivity. Our studies suggest a novel role for sGP as a structural protein.