Protein-protein interactions (PPIs) control virtually all cellular processes and have
thus emerged as potential targets for development of molecular therapeutics. Peptide-based
inhibitors of PPIs are attractive given that they offer recognition potency and selectivity
features that are ideal for function, yet, they do not predominantly populate the
bioactive conformation, frequently suffer from poor cellular uptake and are easily
degraded, for example, by proteases. The constraint of peptides in a bioactive conformation
has emerged as a promising strategy to mitigate against these liabilities. In this
work, using peptides derived from hypoxia-inducible factor 1 (HIF-1 alpha) together
with dibromomaleimide stapling, we identify constrained peptide inhibitors of the
HIF-1 alpha/p300 interaction that are more potent than their unconstrained sequences.
Contrary to expectation, the increased potency does not correlate with an increased
population of an alpha-helical conformation in the unbound state as demonstrated by
experimental circular dichroism analysis. Rather, the ability of the peptide to adopt
a bioactive alpha-helical conformation in the p300 bound state is better supported
in the constrained variant as demonstrated by molecular dynamics simulations and circular
dichroism difference spectra.