Chemically stabilizing the BimBH3 peptide's helical structure unexpectedly reduced its binding to target proteins and failed to kill cancer cells, challenging assumptions about stapled peptide design.
Reduced affinityThe stapled BimSAHB peptide bound worse to Bcl-2 proteins than the native flexible peptide, despite being locked in the 'active' conformation
What the researchers found
The stapled BimBH3 peptide (BimSAHB), designed to have enhanced α-helical stability and improved binding to pro-survival Bcl-2 proteins, actually showed reduced binding affinity for its targets. The researchers attributed this to disruption of a network of stabilizing intramolecular interactions that exist in the bound state of the native (unstapled) peptide.
Furthermore, cells exposed to BimSAHB did not readily undergo apoptosis, strongly indicating that the stapled peptide is not inherently cell permeable — contradicting a key assumption behind its design as a therapeutic agent.
Why it matters
Stapled peptides are a major strategy in peptide drug development, with several candidates in clinical trials. This study provides an important cautionary finding: locking a peptide into its helical shape doesn't always improve binding and can actually make things worse if it disrupts critical interactions needed for target recognition.
How the study worked
The researchers used binding affinity measurements to compare stapled and native BimBH3 peptides against pro-survival Bcl-2 proteins. Structural analysis identified the intramolecular interaction networks disrupted by stapling. Cell-based apoptosis assays tested whether the modified peptides could kill cells, indirectly testing cell permeability.
What this study cannot tell us
The study focused on one specific stapled peptide (BimSAHB) targeting Bcl-2 family proteins, so the findings may not generalize to all stapled peptides. Different staple positions or chemistries might yield different results. The study did not test whether alternative modifications could improve both stability and binding.
How to read the evidence
This is a rigorous laboratory study published in ACS Chemical Biology combining structural, binding, and cellular assays. The finding is well-supported mechanistically but applies to a single peptide system.
When this study was published
Published in 2013, this study raised early warnings about stapled peptide design assumptions. Its findings remain relevant as the field continues to develop stapled peptide therapeutics.
The bigger picture
This study challenged a widely held assumption in the stapled peptide field — that stabilizing a peptide's helical conformation will enhance its binding and biological activity. The finding that the bound-state conformation requires a flexible network of interactions has influenced subsequent stapled peptide design strategies and highlighted the importance of understanding peptide-target interactions before applying structural modifications.
Questions still open
- Can staple placement be optimized to preserve the critical intramolecular interaction network while still stabilizing the helix?
- How many other stapled peptides in development might suffer from similar reduced-affinity effects?
- What alternative strategies could improve BimBH3 cell permeability without compromising target binding?
Common questions
What are stapled peptides and why are they important?
Why did stabilizing this peptide make it worse?
Read the original research
Stabilizing the pro-apoptotic BimBH3 helix (BimSAHB) does not necessarily enhance affinity or biological activity.
ACS chemical biology, 8(2), 297-302
Citation
Okamoto, Toru; Zobel, Kerry; Fedorova, Anna; Quan, Clifford; Yang, Hong; Fairbrother, Wayne J; Huang, David C S; Smith, Brian J; Deshayes, Kurt; Czabotar, Peter E. (2013). Stabilizing the pro-apoptotic BimBH3 helix (BimSAHB) does not necessarily enhance affinity or biological activity.. ACS chemical biology, 8(2), 297-302. https://doi.org/10.1021/cb3005403