Mechanistic insights into the translocation of full length HIV-1 Tat across lipid membranes

Real-time monitoring the interfacial dynamic processes at model cell membranes: Taking cell penetrating peptide TAT as an example

A real-time and molecule-level monitoring of the interfacial dynamic interactions between molecules and a cell membrane is of vital importance. Herein, taking TAT, one of the most representative cell penetrating peptides, as an example, a photo-voltage transient technique and a dynamic giant bistratal vesicle (GBV) leakage method were combined with the traditional giant unilamellar vesicle (GUV) leakage assays, to provide a molecule-level understanding of the dynamic membrane interaction process performed in a low ionic strength and neutral pH condition. The photo-voltage test based on supported phospholipid bilayers showed a quick disturbance (<1 min) followed by a continuous reconstruction of the membrane by peptides, leading to a slight destruction (at TAT concentrations lower than 1 μg mL^-1, i.e., 0.64 μM) or strong damage (e.g. at 10 μg mL^-1, i.e., 6.4 μM) of the bilayer structure. The GUV/GBV leakage assays further demonstrated the TAT-induced membrane deformation and transmembrane diffusion of dyes, which occurred in an immediate, linear, and TAT-concentration dependent manner. Moreover, the flux of dye across the substrate-immobilized membranes was approximately three times of that across the substrate-free ones. This work gives information on time and molecular mechanism of the TAT-membrane interactions, demonstrates the different permeabilizing effects of TAT on immobilized and free membranes. Overall, it provides useful strategies to investigate the nano-bio interfacial interactions in a simple, global and real-time way.

Fundamental molecular mechanism for the cellular uptake of guanidinium-rich molecules

Guanidinium-rich molecules, such as cell-penetrating peptides, efficiently enter living cells in a non-endocytic energy-independent manner and transport a wide range of cargos, including drugs and biomarkers. The mechanism by which these highly cationic molecules efficiently cross the hydrophobic barrier imposed by the plasma membrane remains a fundamental open question. Here, a combination of computational results and in vitro and live-cell experimental evidence reveals an efficient energy-independent translocation mechanism for arginine-rich molecules. This mechanism unveils the essential role of guanidinium groups and two universal cell components: fatty acids and the cell membrane pH gradient. Deprotonated fatty acids in contact with the cell exterior interact with guanidinium groups, leading to a transient membrane channel that facilitates the transport of arginine-rich peptides toward the cell interior. On the cytosolic side, the fatty acids become protonated, releasing the peptides and resealing the channel. This fundamental mechanism appears to be universal across cells from different species and kingdoms.