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.