Cell-penetrating HIV1 TAT peptides float on model lipid bilayers

Area of Science:

• Biophysics
• Cell Biology
• Membrane Science

Background:

• Cell-penetrating peptides (CPPs) facilitate molecular transport into cells.
• The translocation mechanism of CPPs across cell membranes remains poorly understood.
• The HIV1 TAT peptide is a well-studied cationic CPP.

Purpose of the Study:

• To investigate the binding and mobility of the HIV1 TAT peptide on model cell membranes.
• To elucidate the biophysical interactions between TAT peptides and lipid bilayers.
• To determine the influence of membrane composition and charge on TAT peptide behavior.

Main Methods:

• Generation of neutral and anionic giant unilamellar vesicles (GUVs) with varying lipid compositions (DPPC, DOPC, cholesterol, DPPS).
• Single-molecule tracking (SMT) of fluorescently labeled lipids and HIV1 TAT peptides.
• Measurement of diffusion coefficients (D) for lipids and peptides in different membrane phases and charge states.

Main Results:

• HIV1 TAT peptides showed efficient binding to anionic GUVs compared to neutral GUVs.
• TAT peptide diffusion on GUV surfaces (D(N,TAT) = 5.3 ± 0.2 µm²/s, D(A,TAT) = 3.3 ± 0.2 µm²/s) was faster than lipid diffusion.
• Peptide diffusion was independent of membrane phase state and peptide concentration, suggesting no aggregation or carpet formation.
• TAT peptides were found to float on lipid bilayers, with deeper immersion into the headgroup domain of anionic lipids.

Conclusions:

• HIV1 TAT peptides interact with lipid bilayers primarily by floating on the surface.
• Membrane charge significantly influences TAT peptide binding and mobility.
• The biophysical mechanism involves electrostatic interactions with anionic lipids, rather than membrane insertion.
• Understanding these interactions is crucial for designing effective CPP-based drug delivery systems.