Driving forces in the delivery of penetratin conjugated G protein fragment

A42 is a chimera peptide consisting of G alpha(s)(374-394)C(379)Athe 21-mer C terminus of the G alpha(s) protein, able of adenosine inhibitory activityand penetratinthe 16 residue fragment, derived from the homeodomain of the Drosophila transcription factor Antennapedia. A42 is able to cross cell membranes and to inhibit A(2A) and A(2B) adenosine and beta-adrenergic receptor stimulated camps (D'Ursi et al. Mol. Pharmacol. 2006, 69, 727-36). Here we present an extensive biophysical study of A42 in different membrane mimetics, with the objective to evaluate the molecular mechanisms which promote the membrane permeation. Fluorescence, CD, and NMR data were acquired in the presence of negatively charged and zwitterionic sodium dodecyl sulfate and dodecylphosphocholine surfactants. To validate the spectroscopic results in a larger scale, fluorescence microscopy experiments were performed on negatively charged and zwitterionic dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylcholine vesicles. Our results show that the internalization of A42 is mainly driven by electrostatic interactions, hydrophobic interactions playing only a secondary, sinergistic role. The distribution of the charges along the molecule has an important role, highlighting that internalization is a process which requires a specific matching of peptide and membrane properties.