Cooperative Nonbonded Forces Control Membrane Binding of the pH-Low Insertion Peptide pHLIP

Abstract

Peptides with the ability to bind and insert into the cell membrane have immense potential in biomedical applications. pH (low) insertion peptide (pHLIP), a water-soluble polypeptide derived from helix C of bacteriorhodopsin, can insert into a membrane at acidic pH to form a stable transmembrane a-helix. The insertion process takes place in three stages: pHLIP is unstructured and soluble in water at neutral pH (state I), unstructured and bound to the surface of a membrane at neutral pH (state II), and inserted into the membrane as an a-helix at low pH (state III). Using molecular dynamics simulations, we have modeled state II of pHLIP and a fast-folding variant of pHLIP, in which each peptide is bound to a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer surface. Our results provide strong support for recently published spectroscopic studies, namely that pHLIP preferentially binds to the bilayer surface as a function of location of anionic amino acids and that backbone dehydration occurs upon binding. Unexpectedly, we also observed several instances of segments of pHLIP folding into a stable helical turn. Our results provide a molecular level of detail that is essential to providing new insights into pHLIP function and to facilitate design of variants with improved membrane-active capabilities.

Ions Modulate Key Interactions between pHLIP and Lipid Membranes

“…Essentially, as more sodium ions are coordinated with C t residues of pHLIP, D14 has an increased availability as a complementary partner to the positively charged R11. This type of interaction is a hallmark of peptide folding and a phenomena that transiently occurs in our previous simulations of pHLIP (42,43). When combined with our analysis of the radius of gyration of pHLIP, these data sug-gest that Na þ binding to the carboxylates of the C t acidic residues contributes to the observed pK changes.…”

Integrated Design of a Membrane‐Lytic Peptide‐Based Intravenous Nanotherapeutic Suppresses Triple‐Negative Breast Cancer

“…Our goal here was to explore neutral (i.e., zwitterionic) and anionic sequences in order to improve targeting of the subtle changes in lipid composition and surface‐pH of malignant cell plasma membranes. We hypothesize that cancer membrane selectivity of membrane‐lytic peptides may be enhanced with the purposeful introduction of anionic residues, [ 14 , 64 , 65 ] which remain a largely unexplored targeting modality among ACPs. The deliberate addition of anionic amino acids was also aimed at addressing the in vivo delivery challenges of overly cationic peptides, [ 9 , 66 ] which have been associated with poor pharmacokinetics and toxicity concerns.…”

Targeting Acidic Diseased Tissues by pH-Triggered Membrane-Associated Peptide Folding

“…In addition, peptide adsorption to the membrane is modulated by membrane composition (Kyrychenko et al, 2015;Karabadzhak et al, 2018;Vasquez-Montes et al, 2018) and the local ionic environment (Schlebach, 2019;Vasquez-Montes et al, 2019;Westerfield et al, 2019). Significant attention has been given to the conformational states of pHLIPs adsorbed by membranes (Brown et al, 2014;Gupta et al, 2018;Vasquez-Montes et al, 2018). Such studies are challenged by the fact that pHLIPs do not adopt unique structures at the membrane surfaces, and a large variety of conformations is possible and dependent on individual pHLIP sequences (Wyatt et al, 2018b) or lipid compositions (Kyrychenko et al, 2015;Vasquez-Montes et al, 2018).…”