Driving forces in the delivery of penetratin conjugated G protein fragment.

A42 is a chimera peptide made up of Gαs(374-394)C379A, the 21-mer C terminus of the Gαs protein endowed with adenosine inhibitory activity and penetratin, the 16 residue fragment, derived from the homeodomain of the Drosophila transcription factor Antennapedia. We previously designed and synthesized this peptide to promote the delivery of the Gαs fragment inside the cell. A42 was shown to be able to cross HMEC-1 and PC12 cell plasma membranes, and to inhibit A2A, A2B adenosine and β-adrenergic receptor stimulated camps. Preliminary conformational data related the penetrating capability of A42 to its structural properties. In the attempt to define the main physical-chemical forces which are the basis of the peptide-membrane interaction and then drive the delivery process, we performed a biophysical characterization of A42 in different membrane mimicking environments using a combined experimental strategy. Zwitterionic and negatively charged micelles, as well as zwitterionic and negatively charged vesicles were investigated by fluorescence, circular dichroism, NMR spectroscopy and by fluorescence microscopy. The data show the importance of the hydrophobic interface in generating and stabilizing the conformational preference of the peptide. In particular the electrostatic properties of the micelle and vesicle surfaces appear to be pivotal for the exposition of the residue side chains that favour the vehiculating and the biological properties of the peptide.