Fig. 1.

S proteins of North/West- and West-African MERS-CoV isolates from dromedary camels are robustly expressed in human cells and efficiently incorporated into viral particles.

(A) Domain organization of the MERS-S proteins studied here. Black arrowheads indicate amino acid variations found in S proteins of African viruses as compared to the S protein of the prototypic Arabian MERS-CoV strain, human betacoronavirus 2c EMC/2012 (GenBank: JX869059.2). Abbreviations: SP = signal peptide, RBD = receptor binding domain, FP = fusion peptide, HR1/HR2 = heptad repeat 1/2, TD = transmembrane domain. (B) The indicated S proteins were transiently expressed in 293T cells, whole cell lysates (WCL) were prepared at 48 h posttransfection and S protein expression was analyzed via Western blot, using an antibody targeting the C-terminal V5-tag. Cells expressing no S protein were used as negative control and detection of β-actin (ACTB) served as loading control. Similar results were obtained in two separate experiments. (C) Rhabdoviral transduction vectors (VSVpp) harboring the indicated S proteins were concentrated by centrifugation and, following lysis, analyzed by Western blot for S protein incorporation, using an antibody targeting the C-terminal V5-tag. Transduction vectors harboring no S protein were used as negative controls and detection of vesicular stomatitis virus matrix protein (VSV-M) served as loading control. Similar results were obtained in a separate experiment. Numbers on the left side of each blot indicate the molecular weight in kilodalton (kDa). Further, bands representing the precursor S protein (S0, black circle) and the S2 subunit of proteolytically processed S protein (grey circle) are indicated.