Cloning, Expression and Purification of Recombinant Forms of Full Length and Extracellular Domain EBOV Glycoprotein within Mammalian Cell-Lines

Background: Full length Ebolavirus glycoprotein (GP) intersperses the outer most lipid membrane to form spikes, where it mediates virus-host cell interaction. A secretory form of GP (sGP) is also produced by all 5 known Ebolavirus species. These attributes make GP an ideal target for research and development (R and D) of Ebolavirus and possibly pan-filovirus targeted Rapid Diagnostic Tests (RDTs), bio-therapeutics and vaccines. Prior cloning of recombinant Zaire ebolavirus (EBOV) GP has majorly used insect (baculovirus ) expression systems. We report the cloning, expression and purification of the full length and extracellular domain (ECD) forms of recombinant EBOV GP in mammalian cell-lines. Methods and results: 2034 and 1956 base-pair (bp) coding DNA sequences corresponding to the 669 and 643 amino acids (aa) residues of full length and ECD forms of EBOV GP were sub-cloned into the pTGE plasmids. Recombinant pTGE-plasmids were used to transfect 293-6E HEK mammalian cells grown in serum-free FreeStyleTM 293 Expression Medium. Cell lysates and or culture supernatants were used to obtain purified protein, followed by analysis on SDS-PAGE and Western blot. Purified full length GP was detected as membrane bound protein in cell lysates with estimated molecular weight of ~100 kDa (Cal.M.W.~71.67 kDa) on Western blot; and 0.02 mg GP (Concentration: 0.2 mg/mL, Purity: ~50%) derived. On the contrary, ECD GP was detected in supernatants of cell culture broth with estimated molecular weights of ~116 kDa based on SDS-PAGE and Western blot; and 1.6 mg (Concentration: 0.4 mg/ml, Purity: ~70%) of GP_ECD was obtained. Conclusion: Within mammalian cells, recombinant full length EBOV GP is predominantly expressed as transmembrane protein (tGP), while ECD GP is eluted into the culture medium. Both recombinant forms of GP are critical for the R and D of rapid diagnostic tests (RDTs).