Figure 1.

Structural analysis of the SQT scaffold presenting four different pro-apoptotic BH3 domains. (a) Amino-acid sequence of the four BH3 peptides used in this study. In the Puma sequence, the underlined amino acids are deleted in pepPumaDel. (b) Nuclear magnetic resonance (NMR) structure of Stefin A (adapted from pdb ref: 1DVC). The three sites for peptide presentation in the SQT peptide aptamer scaffold are highlighted in red. (c) The CD spectrum of SQT alone and with N-terminal insertions of the HA tag (a negative control not expected to adopt an alpha helical configuration) or with each BH3 peptide. The single inflection point around 218 nm indicates predominantly β-strands in the SQT and SQT-HA spectra. A shift in the inflection point to 220–222 nm, the deeper inflection of the spectrum and an additional shoulder signal the alpha helix formed by the BH3 peptides. SQT with Noxa BH3 and the HA peptide have been reported previously²³