Data from: A fusion protein’s weak link: functional constraints revealed by inhibitory peptide interaction with the parainfluenza fusion protein

Human parainfluenza viruses (HPIVs) cause significant respiratory
illnesses including croup and pneumonia. HPIV infection begins with fusion
of viral and host cell membranes, driven by the coordinated actions of the
attachment (HN) and fusion (F) glycoproteins, which together form the
fusion/entry complex. We have described fusion inhibitory peptides derived
from the heptad repeat (HRC) domain of the F glycoprotein with potent
antiviral activity against HPIV3 and other paramyxoviruses. These peptides
inhibit fusion by binding to the transiently exposed N-terminal heptad
repeat (HRN) segments of the F prehairpin intermediate and preventing the
six-helix bundle (6HB) formation that is required for the membrane fusion
process. We report viral variants that escape inhibition by an
α/β-substituted HRC peptide of HPIV3 through an HN mutation that enhances
HN’s activation of F, and a mutation in F’s HRN domain that destabilizes
the 6HB. The F HRN domain bearing the alteration shows reduced α-helicity
relative to the wildtype HRN and forms an assembly with the HRC domain
that is destabilized relative to the wildtype 6HB. This viral variant is
not resistant to an HRC-derived α-peptide inhibitor that forms a more
stable 6HB relative to the HRC-derived α/β-peptide. The emergence of this
variant suggests that improved inhibitor potency against HPIV3 could be
achieved by increasing the stability of the α/β-peptide/HRN 6HB. The
unique mutation in F that reduces sensitivity to inhibitor also
compromises viral fitness in a human airway model and impairs viral
infection, presumably as a result of diminished post-fusion state
stability.