Role of Membrane Potential and Hydrogen Bonding in the Mechanism of Translocation of Guanidinium-Rich Peptides into Cells

Abstract

The results described herein support a mechanistic hypothesis for how guanidine-rich transporters attached to small cargos (MW ca. <3000) can migrate across the lipid membrane of a cell and directly enter the cytosol. Arginine oligomers are found to partition almost completely into the aqueous layer of a water-octanol bilayer. However, when the same partitioning experiment is conducted in the presence of sodium laurate, a representative negatively charged membrane constituent, the arginine oligomer partitions almost completely (>95%) into the octanol layer. In contrast, ornithine oligomers partition almost exclusively into the water layer with and without added sodium laurate. The different partitioning between guanidinium-rich and ammonium-rich oligomers in the presence of sodium laurate is consistent with the ability of the former to form a bidentate hydrogen bonded ion pair. Mono- and dimethylated arginine oligomers, which like ornithine can only efficiently form monodentate hydrogen bonds, were prepared and found to exhibit poor cellular uptake. Ion pair formation converts a once water-soluble agent to a lipid-soluble agent, thereby reducing the energetic penalty for passage of guanidine-rich transporters through the lipid bilayer. Uptake of guanidine-rich transporters is known to be an energy-dependent process, and this requirement for cellular ATP is now rationalized by the inhibition of guanidine-rich transporter uptake in the presence of agents that reduce the membrane potential. Specifically, incubation of cells in buffers with high potassium ion concentrations or pretreatment of cells with gramicidin A reduces the cellular uptake of Fl-aca-arg8-CONH2 by >90%. Furthermore, the reciprocal experiment of hyperpolarizing the cell with valinomycin increased uptake by >1.5 times. In summary, we propose that the water-soluble, positively charged guanidinium headgroups of the transporter form bidentate hydrogen bonds with H-bond acceptor functionality on the cell surface. The resultant ion pair complexes partition into the lipid bilayer and migrate across at a rate related to the membrane potential. The complex dissociates on the inner leaf of the membrane, and the transporter enters the cytosol. This hypothesis does not preclude uptake by other mechanisms, including endocytosis, which is likely to dominate with large cargos.

Structure and dynamics of cationic membrane peptides and proteins: Insights from solid‐state NMR

“…98 Other protein-derived or chemically synthesized CPPs such as polyarginines have also been characterized. 99,100 Because of the highly charged nature of CPPs, the same free-energy question for AMPs is also relevant for CPPs. Structural studies of CPPs when bound to lipid membranes thus provide valuable insights into their mechanism of membrane translocation.…”

Internalization of cationic peptides: the road less (or more?) traveled

“…The favorable Coulombic component makes such hydrogen bonds especially strong [19]. Using N-methylated arginine residues, Rothbard and coworkers have elegantly demonstrated that the ability of the guanidinium group to form hydrogen bonds is indeed essential for efficient cellular uptake [20,21].…”

Real-time analysis of uptake and bioactivatable cleavage of luciferin-transporter conjugates in transgenic reporter mice

“…Many types of transporters have been reported in recent years including peptides (1)(2)(3)(4)(5), peptoids (6), polyamines (7,8), oligocarbamates (9), dendrimers (10,11), polysaccharides (12), steroids (13), cationic lipids (14,15), guanidinoglycosides (16), and even nanotubes (17). These transporters operate through a variety of mechanisms and some through multiple mechanisms depending on cell type, cargo, and other variables (5,(18)(19)(20)(21)(22). Among the classes of transporters, oligoguanidine based transporters are particularly promising, providing excellent water solubility and at the same time the remarkable ability to rapidly cross the nonpolar membrane of a cell.…”