Sequence motif upstream of the Hendra virus fusion protein cleavage site is not sufficient to promote efficient proteolytic processing

The Hendra virus fusion (HeV F) protein is synthesized as a precursor, F0, and proteolytically cleaved into the mature F1 and F2 heterodimer, following an HDLVDGVK109 motif. This cleavage event is required for fusogenic activity. To determine the amino acid requirements for processing of the HeV F protein, we constructed multiple mutants. Individual and simultaneous alanine substitutions of the eight residues immediately upstream of the cleavage site did not eliminate processing. A chimeric SV5 F protein in which the furin site was substituted for the VDGVK109 motif of the HeV F protein was not processed but was expressed on the cell surface. Another chimeric SV5 F protein containing the HDLVDGVK109 motif of the HeV F protein underwent partial cleavage. These data indicate that the upstream region can play a role in protease recognition, but is neither absolutely required nor sufficient for efficient processing of the HeV F protein.