Stabilizing the Pro-Apoptotic BimBH3 Helix (BimSAHB) Does Not Necessarily Enhance Affinity or Biological Activity

Abstract

An attractive approach for developing therapeutic peptides is to enhance binding to their targets by stabilizing their α-helical conformation, for example, stabilized BimBH3 peptides (BimSAHB) designed to induce apoptosis. Unexpectedly, we found that such modified peptides have reduced affinity for their targets, the pro-survival Bcl-2 proteins. We attribute this loss in affinity to disruption of a network of stabilizing intramolecular interactions present in the bound state of the native peptide. Altering this network may compromise binding affinity, as in the case of the BimBH3 stapled peptide studied here. Moreover, cells exposed to these peptides do not readily undergo apoptosis, strongly indicating that BimSAHB is not inherently cell permeable.

Absence of a Stable Secondary Structure Is Not a Limitation for Photoswitchable Inhibitors of β-Arrestin/β-Adaptin 2 Protein-Protein Interaction

“…Despite the contrasts with the b-arrestin/b-adaptin 2 PPI and with our recommendations, we share the interpretation that the stabilization of a helices is not a requirement for the design of peptide inhibitors (photoswitchable or not) of PPIs mediated by a helix. Regarding this issue, another study questions the effect of stabilization of the helix by stapling in the BimBH3/Bcl-2 PPI (Okamoto et al, 2013), a classic example where stapled peptides were tested previously (Walensky et al, 2004).…”

Stapled peptide design: principles and roles of computation

“…No direct correlation was also found between helical content and cell activity in another study on the targeting of HIV-1 integrase by hydrocarbon stapled peptides [27]. Stapling also does not always improve the binding affinity of the peptide, as observed in several independent studies [40,[95][96][97]. Enthalpy-entropy compensation has recently been invoked to explain these perplexing observations [97].…”

Regulation of protein–protein interactions using stapled peptides

“…The BIM BH3 all-hydrocarbon stapled peptide did not in fact induce apoptosis much more than the native sequence and was also not inherently cell permeable. 71 In addition, a lactam-stapled peptide based on the same helical sequence was found to have a greater percentage of helicity than the all-hydrocarbon staple.…”

“…71 However, in their hands, the stapling of the peptide did not enhance its affinity or biological activity. The BIM BH3 all-hydrocarbon stapled peptide did not in fact induce apoptosis much more than the native sequence and was also not inherently cell permeable.…”