PROCESSING OF THE EBOLA-VIRUS GLYCOPROTEIN BY THE PROPROTEIN CONVERTASE FURIN

in the present study, we have investigated processing and maturation o f the envelope glycoprotein (GP) of Ebola virus. When GP expressed fro m vaccinia virus vectors was analyzed by pulse-chase experiments, the mature form and two different precursors were identified. First, the e ndoplasmic reticulum form preGP(er), full length GP with oligomannosid ic N-glycans, was detected, preGP(er) (IIO kDa) was replaced by the Go lgi-specific form preGP (160 kDa), full-length GP containing mature ca rbohydrates, preGP was finally converted by proteolysis into mature GP (1,2), which consisted of two disulfide-linked cleavage products, the aminoterminal 140-kDa fragment GP(1), and the carboxyl-terminal 26-kDa fragment GP(2). GP(1,2) was also identified in Ebola virions. Studies employing site-directed mutagenesis revealed that GP was cleaved at a multibasic amino acid motif located at positions 497 to 501 of the OR F. Cleavage was blocked by a peptidyl chloromethylketone containing su ch a motif, CP is cleaved by the proprotein convertase furin. This was indicated by the observation that cleavage did not occur when GP was expressed in furin-defective LoVo cells but that it was restored in th ese cells by vector-expressed furin. The Reston subtype, which differs from all other Ebola viruses by its low human pathogenicity, has a re duced cleavability due to a mutation at the cleavage site. As a result of these observations, it should now be considered that proteolytic p rocessing of GP may be an important determinant for the pathogenicity of Ebola virus.