β-Glutamine-mediated Self-Association of Transmembrane β- Peptides within Lipid Bilayers
U. Rost, C. Steinem, U. Diederichsen
Transmembrane β-peptide helices and their association in lipid membranes are still widely unexplored. We designed and synthesized transmembrane β-peptides harboring different numbers of D-β3 -glutamine residues (h Gln) by solid phase peptide synthesis. By means of circular dichroism spectroscopic measurements, the secondary structure of the β-peptides reconstituted into unilamellar vesicles was determined to be similar to a right-handed 314-helix. Fluorescence spectroscopy using D-β3 -tryptophan residues strongly suggested a transmembrane orientation. Two respectively three h Gln served as recognition units between the helices to allow helix-helix assembly driven by hydrogen bond formation. The association state of the transmembrane β-peptides as a function of the number of h Gln residues was investigated by fluorescence resonance energy transfer (FRET). Therefore, two fluorescence probes (NBD, TAMRA) were covalently attached to the side chains of the transmembrane β-peptide helices. The results clearly demonstrate that only β-peptides with h Gln as recognition units assemble into oligomers, presumably trimers. Temperature dependent FRET experiments further show that the strength of the helix-helix association is a function of the number of h Gln residues in the helix.
Circular dichroism, Secondary structure, Vesicle interactions, Thermal stability, Biochemistry