Examination of the role of histidine residues proximal to the cleavage site on cathepsin L processing of the Hendra virus fusion protein

Abstract

The recently emerged Hendra virus is an enveloped, single-stranded, negative-sense RNA virus which is classified as a BSL-4 pathogen. Both the viral attachment (G) and fusion (F) proteins are required for fusion of the viral membrane with the host cell membrane, an obligate early step in infection. Hendra F must undergo proteolytic processing to be fusogenically active, and this unique cleavage event involves trafficking of F to the plasma membrane and subsequent endocytosis and cleavage by the endosomal/lysosomal protease cathepsin L. While cleavage of other paramyxovirus fusion proteins occurs following specific sequences, cathepsin L lacks a specific substrate recognition sequence. As Hendra F cleavage by cathepsin L occurs in acidic endosomal compartments, protonation of residues near the cleavage site could modulate F cleavage. The ectodomain of F contains only two histidine residues, H102 and H372. Mutation of H102, directly upstream of the cleavage site, to an alanine did not significantly alter cleavage or function. Modeling Hendra F on to the prefusion structure of HPIV5 F indicates that H372 is in close proximity to H102, thus local conformational changes driven by histidine protonation could alter the cleavage site. We will therefore examine processing and function of the Hendra F mutants H372A and H102A/H372A to define the possible role of histidine protonation in Hendra F cleavage. This work is supported by grants from the National Institutes of Health and the March of Dimes.