Transmembrane β-peptide helices as molecular rulers at the membrane surface.

β-Peptides are known to form 14-helices with high conformational rigidity, helical persistence length, and well-defined spacing and orientation regularity of amino acid side chains. Therefore, β-peptides are well suited to serve as backbone structures for molecular rulers. On the one hand, they can be functionalized in a site-specific manner with molecular probes or fluorophores, and on the other hand, the β-peptide helices can be recognized and anchored in a biological environment of interest. In this study, the β-peptide helices were anchored in lipid bilayer membranes, and the helices were elongated in the outer membrane environment. The distances of the covalently bound probes to the membrane surface were determined using graphene-induced energy transfer (GIET) spectroscopy, a method based on the distance-dependent quenching of a fluorescent molecule by a nearby single graphene sheet. As a proof of principle, the predicted distances were determined for two fluorophores bound to the membrane-anchored β-peptide molecular ruler.