D614G Substitution of SARS-CoV-2 Spike Protein Increases Syncytium Formation and Virus Titer via Enhanced Furin-Mediated Spike Cleavage.

Since the D614G substitution in the spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged, the variant strain has undergone a rapid expansion to become the most abundant strain worldwide. Therefore, this substitution may provide an advantage for viral spreading. To explore the mechanism, we analyzed 18 viral isolates containing S proteins with either G614 or D614 (S-G614 and S-D614, respectively).