Bilayer Elastic Properties Modulate Interface Energetics of Transmembrane β-Barrels.

Quantifying the Energetics of Protein-Mediated Stabilization of Membrane Deformation.

Membrane curvature plays a central role in a wide range of biological processes, yet a quantitative and transferable description of its underlying energetics remains challenging. In this work, we develop a "reaction coordinate" within the Umbrella-Sampling framework to compute the free-energy cost associated with local membrane bending in both coarse-grained and atomistic simulations. The methodology is systematically validated across diverse lipid environments, including pure bilayers with varying tail unsaturation, tail length, and headgroup chemistry, where it reproduces established trends in membrane-mechanical rigidity. Extension to mixed lipid systems further captures composition-dependent modulation of bending energetics, including cholesterol-induced responses. Finally, we apply the framework to membrane-active proteins with distinct curvature-generation mechanisms and demonstrate that the method successfully captures the protein modulation of the free-energy cost of local membrane deformation. Furthermore, the method is transferable to atomistic membrane systems while maintaining reasonable computational efficiency, providing a unified approach for quantifying membrane bending energetics across lipids, proteins, and simulation scales.

Peptide Sequence Features that Reduce Membrane Pore Line Tension

Membrane pore stability is central to many processes involving membrane permeabilization, yet it remains unclear how the sequence of pore-localizing peptides can modify the energetics of the pore boundary. For large pores, the energetic cost associated with increasing pore size is described by the membrane line tension. Peptides capable of reducing line tension can therefore stabilize permeable membrane states, making their identification relevant for the design of membrane-active molecules. Here, we combine coarse-grained molecular dynamics simulations, free energy calculations, and evolutionary optimization algorithms to identify sequence features of α-helical peptides that reduce membrane line tension. The best-performing peptides consistently showed an amphipathic organization with aromatic-rich termini, a hydrophobic/aromatic membrane-facing nonpolar face, and a negatively charged polar face. These sequence features promoted peptide localization at the pore rim close to the intact bilayer and orientation parallel to the membrane edge. This binding geometry reorganized lipids at the pore rim and efficiently reduced the exposure of their hydrophobic tails to water, thereby reducing the energetic cost of the pore boundary. The main sequence and mechanistic trends identified in coarse-grained simulations were reproduced in all-atom simulations. Together, these results link peptide sequence to pore-rim localization, lipid reorganization, and ultimately line-tension reduction, providing molecular design principles for α-helical peptides that stabilize permeable membrane states.

Lipid-Shell PARCH: A Physically Motivated Scale for Transmembrane Residue Hydropathy

A lipid-shell modification to the protocol for assigning a residue’s character on a hydropathy (PARCH) scale is presented, in which the protein’s first hydration shell is enclosed by a lipid boundary layer during thermal annealing to establish a computationally affordable and physically meaningful approach to quantifying membrane hydropathy that is sensitive to residue identity, membrane depth, and cooperative hydration among tandem charged residues.

Modulation of the phospholipid dynamics and bilayer water accessibility with the membrane-associated nucleation of β-amyloid (Aβ) peptides.

Observations suggest a general rigidification of bilayers upon instant Aβ-bilayer interactions across different bilayer phospholipid compositions and Aβ isoforms, accompanied by increase of water accessibility to bilayer interiors, and establish a molecular-level, schematic explanation of the membrane-associated Aβ nucleation process.

Energetics of stalk intermediates elucidated from hydrostatic pressure effects on membrane fusion

Membrane fusion is an essential process in cells that requires a balance of lipid composition to establish biophysical properties conducive to topology changes. During fusion, lipids of opposing membranes must invert and overcome energy barriers associated with forming highly curved stalk and pore intermediates. While theoretical work has modelled the effect of lipid intrinsic curvature on stalk formation, quantifying the relationship experimentally has proven to be a challenge due to the inability to vary lipid curvature without concomitantly changing other properties that affect fusion. Here we address this hurdle by using hydrostatic pressure to modulate lipid intrinsic curvature independently of chemical composition. Using high-pressure stopped-flow fluorimetry, we measured rates of calcium-mediated lipid mixing between populations of vesicles, a process that is strongly inhibited by pressure. We correlated mean lipid intrinsic curvature across pressure with lipid mixing rates by incorporating complementary small-angle x-ray scattering measurements for each individual lipid component. This analysis showed that lipid mixing rates, a proxy for hemifusion, across compositional and pressure regimes are determined by changes in lipid spontaneous curvature. Consistent with previous theoretical models, we find a linear relation between lipid intrinsic curvature and the hemifusion stalk formation energy, offering direct experimental support for the stalk hypothesis. Significance statement Membrane fusion proceeds through a hemifusion stalk intermediate whose formation energy depends on lipid intrinsic curvature, a central prediction of the stalk hypothesis that has lacked direct experimental support. Previous tests relied on changes in lipid composition that affect multiple membrane properties, confounding the contribution of curvature alone. Here we use hydrostatic pressure to tune lipid curvature independently of chemical composition and calibrate its effects with high-pressure SAXS. Hemifusion rates across three lipid compositions and four pressures collapse into a single exponential dependence on mean spontaneous curvature, yielding a linear relation between curvature and energy consistent with continuum elastic theory. This work quantifies how lipid composition tunes fusion kinetics, suggesting that small changes in lipid curvature may strongly affect fusogenicity.

Water at Lipid Interfaces: Domains and Defects.