Conformational and Associative Behaviours of the Third Helix of Antennapedia Homeodomain in Membrane‐Mimetic Environments

The third helix of antennapedia homeodomain pAntp‐(43–58) can translocate through cell membrane and has been used as an intracellular vehicle for delivering peptides and oligonucleotides. The conformational and associative behaviour of two peptidic vectors pAntp‐(43–58) and [Pro50]pAntp‐(43–58) has been analyzed by different biophysical methods. pAntp‐(43–58) adopts an amphipathic helical structure in 30% (by vol.) hexafluoroisopropanol, in perfluoro‐ tert ‐butanol and in the presence of SDS micelles. CD spectra indicate that the conformation of [Pro50]pAntp‐(43–58) in contrast to pAntp‐(43–58) is independent of the media used. 1 H‐NMR spectroscopy in SDS micelles or in perfluoro‐ tert ‐butanol allows detection of aggregated peptides probably in a ribbon 2 7 type conformation. These conformations became the predominant structure when Gln50 was replaced by Pro50. Interproton‐distance restraints derived from NOE measurements have been classified in two groups corresponding to two types of structures: α‐helix and essentially extended structures. Consecutive CHα( i )/CHα( i +1) NOES are only compatible with aggregates. Simulated annealing calculation of dimeric structure agrees with φ and ψ angles in the β‐sheet and γ‐turn regions. Fluorescence spectroscopy analysis has shown that the indole groups of both peptides penetrate into SDS micelles; both peptides also induce the formation of micelles at very low concentration of SDS (20 μM). Similar interaction was observed with reverse‐phase micelles made of bis(2‐ethyhexyl) sodium sulfosuccinate and small unilamellar vesicles (SUV) made of a mixture of phosphatidylcholine/phosphatidylserine. 31 P‐NMR of vesicles (SUV and large unilamellar vesicles) indicated that the addition of pAntp analogues did not affect the size of phosphatidylcholine/phosphatidylserine vesicles. The addition of pAntp analogues to lipidic dispersions modulates lipid polymorphism in different ways depending on the mixtures of acidic lipids.