Amphiphilic peptides containing alternating α-aminoxy acids and α-amino acids to mimic the α-helix of bak BH3 domain and disulfide bondas covalent linkage for stabilizing 7/8 helix

Abstract

The binding between the survival protein Bcl-xL and the death-promoting region of

the Bcl-2-related protein Bak is one of the key protein-protein interactions in the

regulation of programmed cell death (apoptosis). Since it is well recognized that the

BH3 domain of Bak adopts an amphipathic α-helix to interact with Bcl-xL through

hydrophobic and electrostatic effects, conformational studies and possible

applications of the α-aminoxy acid-containing peptides as mimics of the α-helix of

Bak BH3 domain have been carried out. The main results are summarized below.

Four short peptides ZT1?ZT4 containing alternating α-aminoxy acids/α-amino acids

as the mimics of the α-helix of Bak protein were designed and synthesized. However,

none of these four peptides, at the concentration of 25 μM, exhibited a significant

inhibitory effect on the Bcl-xL inhibition test. Circular dichroism spectroscopic

studies on ZT1?ZT4 as well as short model peptides N-minus, N-plus, C-minus and

C-plus suggest that the proposed secondary structure, the 7/8 helix, is not stable in

aqueous solutions.

1H NMR, 2D NMR and circular dichroism spectroscopic studies on the disulfide

bond-constrained short peptides 4.7?4.9 with alternating α-aminoxy acids and

α-amino acids suggest that a disulfide linker with three methylene units between

adjacent α-amino acid residues could dramatically increase the stability of the 7/8

helix even in a mixed buffer/methanol solution.

1H NMR, 2D NMR and circular dichroism spectroscopic studies have also revealed

that the hybrid soluble peptides C-free, N-free and Both-free containing α-amino

acids and β-2,2-cyclopropyl-amino acids adopted a stable 8/8 helix in aqueous

solution.