Probing the interactions of the HIV-1 matrix protein-derived polybasic region with lipid bilayers: insights from AFM imaging and force spectroscopy

The human immunodeficiency virus type 1 (HIV-1) matrix protein contains a highly basic region, MA-HBR, crucial for various stages of viral replication. To elucidate the interactions between the polybasic peptide MA-HBR and lipid bilayers, we employed liquid-based atomic force microscopy (AFM) imaging and force spectroscopy on lipid bilayers of differing compositions. In 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers, AFM imaging revealed the formation of annulus-shaped protrusions upon exposure to the polybasic peptide, accompanied by distinctive mechanical responses characterized by enhanced bilayer puncture forces. Importantly, our AFM-based force spectroscopy measurements unveiled that MA-HBR induces interleaflet decoupling within the cohesive bilayer organization. This is evidenced by a force discontinuity observed within the bilayer's elastic deformation regime. In POPC/cholesterol bilayers, MA-HBR caused similar yet smaller annular protrusions, demonstrating an intriguing interplay with cholesterol-rich membranes. In contrast, in bilayers containing anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) lipids, MA-HBR induced unique annular protrusions, granular nanoparticles, and nanotubules, showcasing its distinctive effects in anionic lipid-enriched environments. Notably, our force spectroscopy data revealed that anionic POPS lipids weakened interleaflet adhesion within the bilayer, resulting in interleaflet decoupling, which potentially contributes to the specific bilayer perturbations induced by MA-HBR. Collectively, our findings highlight the remarkable variations in how the polybasic peptide, MA-HBR, interacts with lipid bilayers of differing compositions, shedding light on its role in host membrane restructuring during HIV-1 infection.