Figure S1 - Role of the Spike Glycoprotein of Human Middle East Respiratory Syndrome Coronavirus (MERS-CoV) in Virus Entry and Syncytia Formation

Detection of trypsin-cleaved MERS-CoV S protein on pseudovirions by antibody to MHV S protein. Pseudovirions containing either MERS-CoV S protein or no spike (control) were incubated with 20 µg/ml of trypsin either at 4°C or 37°C for 20 min. After digestion, glycoproteins on pseudovirions were analyzed by immunoblot using AO4 antibody to the S protein of murine betacoronavirus MHV-A59 that cross-reacts with MERS-CoV S protein. Lanes 1 to 3: No spike control; Lanes 4 to 6: MERS pseudovirions; Lanes 1 and 4: No trypsin; Lanes 2 and 5: trypsin at 4°C; Lane 3 and 5: trypsin at 37°C. The band at ~90kDa was seen in pseudovirions without spike, indicating that it is not due to MERS-CoV S protein. Uncleaved MERS-CoV S protein, ~200kDa, on pseudovirions is shown in lane 4, and trypsin treatment cleaved all of the S protein, and generated a subunit of ~65kDa that was recognized by AO4 antibody (Lanes 5 and 6). (EPS)