Formation and Maintenance of Tubular Membrane Projections Require Mechanical Force, but their Elongation and Shortening do not Require Additional Force

Membrane tubulation induced by a bacterial glycolipid

Membrane protein integrase (MPIase) is a glycolipid found in Escherichia coli cell membranes. It consists of diacylglycerol and a sugar chain comprising approximately 10 repeating trisaccharide units, made up of three types of N-acetylated amino sugars linked by pyrophosphate. In cooperation with proteinaceous translocons, MPIase regulates membrane protein integration. In this study, using various microscopic techniques, we demonstrated that externally added MPIase induces the formation of a single tubule protruding outward from giant unilamellar vesicles (GUVs). These tubules resembled those reported in studies involving membrane-perturbing proteins but differed in that MPIase formed aggregates at the base of the tubules. We also showed that hydrophobic interactions between longer sugar chains of MPIase play a key role in forming multiple aggregates on the membrane, which in turn induce membrane budding and triggers membrane protrusion. Once a single tubule begins to form from one of the aggregates, elongating a longer and narrower tubule can reduce line tension and elastic energy for a given area differences between the internal and external leaflets. These findings provide insights into the mechanism underlying glycolipid-induced membrane tubulation and suggest that the unique long sugar chain of MPIase can offer functions beyond its essential role in membrane protein integration.

Advances in giant unilamellar vesicle preparation techniques and applications

Giant unilamellar vesicles (GUVs) are versatile and promising cell-sized bio-membrane mimetic platforms. Their applications range from understanding and quantifying membrane biophysical processes to acting as elementary blocks in the bottom-up assembly of synthetic cells. Definite properties and requisite goals in GUVs are dictated by the preparation techniques critical to the success of their applications. Here, we review key advances in giant unilamellar vesicle preparation techniques and discuss their formation mechanisms. Developments in lipid hydration and emulsion techniques for GUV preparation are described. Novel microfluidic-based techniques involving lipid or surfactant-stabilized emulsions are outlined. GUV immobilization strategies are summarized, including gravity-based settling, covalent linking, and immobilization by microfluidic, electric, and magnetic barriers. Moreover, some of the key applications of GUVs as biomimetic and synthetic cell platforms during the last decade have been identified. Membrane interface processes like phase separation, membrane protein reconstitution, and membrane bending have been deciphered using GUVs. In addition, vesicles are also employed as building blocks to construct synthetic cells with defined cell-like functions comprising compartments, metabolic reactors, and abilities to grow and divide. We critically discuss the pros and cons of preparation technologies and the properties they confer to the GUVs and identify potential techniques for dedicated applications.

Extensible membrane nanotubules mediate attachment of Trypanosoma cruzi epimastigotes under flow

Trypanosoma cruzi is the etiological agent of Chagas disease, an important cause of infectious chronic myocardiopathy in Latin America. The life cycle of the parasite involves two main hosts: a triatomine (arthropod hematophagous vector) and a mammal. Epimastigotes are flagellated forms inside the triatomine gut; they mature in its intestine into metacyclic trypomastigotes, the infective form for humans. Parasites attach despite the shear stress generated by fluid flow in the intestines of the host, but little is known about the mechanisms that stabilize attachment in these conditions. Here, we describe the effect of varying levels of shear stress on attached T. cruzi epimastigotes using a parallel plate flow chamber. When flow is applied, parasites are partially dragged but maintain a connection to the surface via ~40 nm wide filaments (nanotubules) and the activity of flagella is reduced. When flow stops, parasites return near their original position and flagellar motion resumes. Nanotubule elongation increases with increasing shear stress and is consistent with a model of membrane tether extension under force. Fluorescent probes used to confirm membrane composition also show micron-wide anchoring pads at the distal end of the nanotubules. Multiple tethering accounts for more resistance to large shear stresses and for reduced flagellar movement when flow is stopped. The formation of membrane nanotubules is a possible mechanism to enhance adherence to host cells under shear stress, favoring the continuity of the parasite´s life cycle.

Identifying and Manipulating Giant Vesicles: Review of Recent Approaches

Giant vesicles (GVs) are closed bilayer membranes that primarily comprise amphiphiles with diameters of more than 1 μm. Compared with regular vesicles (several tens of nanometers in size), GVs are of greater scientific interest as model cell membranes and protocells because of their structure and size, which are similar to those of biological systems. Biopolymers and nano-/microparticles can be encapsulated in GVs at high concentrations, and their application as artificial cell bodies has piqued interest. It is essential to develop methods for investigating and manipulating the properties of GVs toward engineering applications. In this review, we discuss current improvements in microscopy, micromanipulation, and microfabrication technologies for progress in GV identification and engineering tools. Combined with the advancement of GV preparation technologies, these technological advancements can aid the development of artificial cell systems such as alternative tissues and GV-based chemical signal processing systems.

Binding of curvature-inducing proteins onto tethered vesicles

A tethered vesicle, which consists of a cylindrical membrane tube and a spherical vesicle, is produced by a mechanical force that is experimentally imposed by optical tweezers and a micropipette. This tethered vesicle is employed for examining the curvature sensing of curvature-inducing proteins. In this study, we clarify how the binding of proteins with a laterally isotropic spontaneous curvature senses and generates the membrane curvatures of the tethered vesicle using mean-field theory and meshless membrane simulation. The force-dependence curves of the protein density in the membrane tube and the tube curvature are reflection symmetric and point symmetric, respectively, from the force point, in which the tube has a sensing curvature. The bending rigidity and spontaneous curvature of the bound proteins can be estimated from these force-dependence curves. First-order transitions can occur between low and high protein densities in the tube at both low and high force amplitudes. The simulation results of the homogeneous phases agree very well with the theoretical predictions. In addition, beaded-necklace-like tubes with microphase separation are found in the simulation.

Liposomal adhesion via electrostatic interactions and osmotic deflation increase membrane tension and lipid diffusion coefficient

Membrane adhesion is a ubiquitous phenomenon in cells and is related to various biological events such as migration, morphogenesis, and differentiation. To understand the physicochemical aspects of membrane adhesion, liposome-liposome adhesion and liposome-substrate adhesion have been studied. Although membrane adhesion has been shown to increase membrane tension and inhibit lipid diffusion, the relationship between these changes and the degree of membrane adhesion have not been quantified. Here, we analyzed the dependence of membrane tension and lipid diffusion on the degree of membrane adhesion, i.e., area fraction of the adherent region. For this purpose, we developed a simple method to prepare adhered liposomes by simple electrostatic interactions between the membranes and by osmotic deflation. We found that the membrane tension of the adhered liposomes increases slightly with an increase in the area fraction of the adherent region. In addition, the lipid diffusion coefficient of the adhered liposomes is larger than that of isolated liposomes, which is consistent with the theoretical prediction. The analysis provides a framework to understand the correlation between cell adhesion and bio-membrane properties such as membrane tension and molecular diffusion.

Raman Spectroscopy Study of Curvature-Mediated Lipid Packing and Sorting in Single Lipid Vesicles

Cellular plasma membrane deformability and stability is important in a range of biological processes. Changes in local curvature of the membrane affect the lateral movement of lipids, affecting the biophysical properties of the membrane. An integrated holographic optical tweezers and Raman microscope was used to investigate the effect of curvature gradients induced by optically stretching individual giant unilamellar vesicles (GUVs) on lipid packing and lateral segregation of cholesterol in the bilayer. The spatially resolved Raman analysis enabled detection of induced phase separation and changes in lipid ordering in individual GUVs. Using deuterated cholesterol, the changes in lipid ordering and phase separation were linked to lateral sorting of cholesterol in the stretched GUVs. Stretching the GUVs in the range of elongation factors 1-1.3 led to an overall decrease in cholesterol concentration at the edges compared to the center of stretched GUVs. The Raman spectroscopy results were consistent with a model of the bilayer accounting for cholesterol sorting in both bilayer leaflets, with a compositional asymmetry of 0.63 ± 0.04 in favor of the outer leaflet. The results demonstrate the potential of the integrated holographic optical tweezers-Raman technique to induce deformations to individual lipid vesicles and to simultaneously provide quantitative and spatially resolved molecular information. Future studies can extend to include more realistic models of cell membranes and potentially live cells.

Ballistic impact response of lipid membranes

Therapeutic agent loaded micro and nanoscale particles as high-velocity projectiles can penetrate cells and tissues, thereby serving as gene and drug delivery vehicles for direct and rapid internalization. Despite recent progress in developing micro/nanoscale ballistic tools, the underlying biophysics of how fast projectiles deform and penetrate cell membranes is still poorly understood. To understand the rate and size-dependent penetration processes, we present coarse-grained molecular dynamics simulations of the ballistic impact of spherical projectiles on lipid membranes. Our simulations reveal that upon impact, the projectile can pursue one of three distinct pathways. At low velocities below the critical penetration velocity, projectiles rebound off the surface. At intermediate velocities, penetration occurs after the projectile deforms the membrane into a tubular thread. At very high velocities, rapid penetration occurs through localized membrane deformation without tubulation. Membrane tension, projectile velocity and size govern which phenomenon occurs, owing to their positive correlation with the reaction force generated between the projectile and the membrane during impact. Two critical membrane tension values dictate the boundaries among the three pathways for a given system, due to the rate dependence of the stress generated in the membrane. Our findings provide broad physical insights into the ballistic impact response of soft viscous membranes and guide design strategies for drug delivery through lipid membranes using micro/nanoscale ballistic tools.

Phospholipase Cβ1 induces membrane tubulation and is involved in caveolae formation

Lipid membrane curvature plays important roles in various physiological phenomena. Curvature-regulated dynamic membrane remodeling is achieved by the interaction between lipids and proteins. So far, several membrane sensing/sculpting proteins, such as Bin/amphiphysin/Rvs (BAR) proteins, are reported, but there remains the possibility of the existence of unidentified membrane-deforming proteins that have not been uncovered by sequence homology. To identify new lipid membrane deformation proteins, we applied liposome-based microscopic screening, using unbiased-darkfield microscopy. Using this method, we identified phospholipase Cβ1 (PLCβ1) as a new candidate. PLCβ1 is well characterized as an enzyme catalyzing the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PIP2). In addition to lipase activity, our results indicate that PLCβ1 possessed the ability of membrane tubulation. Lipase domains and inositol phospholipids binding the pleckstrin homology (PH) domain of PLCβ1 were not involved, but the C-terminal sequence was responsible for this tubulation activity. Computational modeling revealed that the C terminus displays the structural homology to the BAR domains, which is well known as a membrane sensing/sculpting domain. Overexpression of PLCβ1 caused plasma membrane tubulation, whereas knockdown of the protein reduced the number of caveolae and induced the evagination of caveolin-rich membrane domains. Taken together, our results suggest a new function of PLCβ1: plasma membrane remodeling, and in particular, caveolae formation.

Reversible Morphological Control of Tubulin-Encapsulating Giant Liposomes by Hydrostatic Pressure

Liposomes encapsulating cytoskeletons have drawn much recent attention to develop an artificial cell-like chemical-machinery; however, as far as we know, there has been no report showing isothermally reversible morphological changes of liposomes containing cytoskeletons because the sets of various regulatory factors, that is, their interacting proteins, are required to control the state of every reaction system of cytoskeletons. Here we focused on hydrostatic pressure to control the polymerization state of microtubules (MTs) within cell-sized giant liposomes (diameters ∼10 μm). MT is the cytoskeleton formed by the polymerization of tubulin, and cytoskeletal systems consisting of MTs are very dynamic and play many important roles in living cells, such as the morphogenesis of nerve cells and formation of the spindle apparatus during mitosis. Using real-time imaging with a high-pressure microscope, we examined the effects of hydrostatic pressure on the morphology of tubulin-encapsulating giant liposomes. At ambient pressure (0.1 MPa), many liposomes formed protrusions due to tubulin polymerization within them. When high pressure (60 MPa) was applied, the protrusions shrank within several tens of seconds. This process was repeatedly inducible (around three times), and after the pressure was released, the protrusions regenerated within several minutes. These deformation rates of the liposomes are close to the velocities of migrating or shape-changing living cells rather than the shortening and elongation rates of the single MTs, which have been previously measured. These results demonstrate that the elongation and shortening of protrusions of giant liposomes is repeatedly controllable by regulating the polymerization state of MTs within them by applying and releasing hydrostatic pressure.

Membrane tubulation from giant lipid vesicles in alternating electric fields

We report on the formation of tubular membrane protrusions from giant unilamellar vesicles in alternating electric fields. The construction of the experimental chamber permitted the application of external AC fields with strength of dozens of V/mm and kHz frequency during relatively long time periods (several minutes). Besides the vesicle electrodeformation from quasispherical to prolate ellipsoidal shape, the formation of long tubular membrane protrusions with length of up to several vesicle diameters, arising from the vesicular surface in the field direction, was registered and analyzed. The threshold electric field at which the electro-induced protrusions appeared was lower than the field strengths inducing membrane electroporation.

Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles

The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

Liposome division by a simple bacterial division machinery

We previously reconstituted Z rings in tubular multilamellar liposomes with FtsZ-YFP-mts, where mts is a membrane-targeting amphiphilic helix. These reconstituted Z rings generated a constriction force but did not divide the thick-walled liposomes. Here we developed a unique system to observe Z rings in unilamellar liposomes. FtsZ-YFP-mts incorporated inside large, unilamellar liposomes formed patches that produced concave distortions when viewed at the equator of the liposome. When viewed en face at the top of the liposome, many of the patches were seen to be small Z rings, which still maintained the concave depressions. We also succeeded in reconstituting the more natural, two-protein system, with FtsA and FtsZ-YFP (having the FtsA-binding peptide instead of the mts). Unilamellar liposomes incorporating FtsA and FtsZ-YFP showed a variety of distributions, including foci and linear arrays. A small fraction of liposomes had obvious Z rings. These Z rings could constrict the liposomes and in some cases appeared to complete the division, leaving a clear septum between the two daughter liposomes. Because complete liposome divisions were not seen with FtsZ-mts, FtsA may be critical for the final membrane scission event. We demonstrate that reconstituted cell division machinery apparently divides the liposome in vitro.

Multiple membrane interactions and versatile vesicle deformations elicited by melittin

Melittin induces various reactions in membranes and has been widely studied as a model for membrane-interacting peptide; however, the mechanism whereby melittin elicits its effects remains unclear. Here, we observed melittin-induced changes in individual giant liposomes using direct real-time imaging by dark-field optical microscopy, and the mechanisms involved were correlated with results obtained using circular dichroism, cosedimentation, fluorescence quenching of tryptophan residues, and electron microscopy. Depending on the concentration of negatively charged phospholipids in the membrane and the molecular ratio between lipid and melittin, melittin induced the “increasing membrane area”, “phased shrinkage”, or “solubilization” of liposomes. In phased shrinkage, liposomes formed small particles on their surface and rapidly decreased in size. Under conditions in which the increasing membrane area, phased shrinkage, or solubilization were mainly observed, the secondary structure of melittin was primarily estimated as an α-helix, β-like, or disordered structure, respectively. When the increasing membrane area or phased shrinkage occurred, almost all melittin was bound to the membranes and reached more hydrophobic regions of the membranes than when solubilization occurred. These results indicate that the various effects of melittin result from its ability to adopt various structures and membrane-binding states depending on the conditions.

The tethered infinitesimal tori and spheres algorithm: a versatile calculator for axisymmetric problems in equilibrium membrane mechanics

Constrained minimization of energy functionals is a central part, and usually the difficult part, of solving problems in the equilibrium mechanics of biological and biomimetic membranes. The inherent difficulties of the conventional variational-calculus approach prevents the numerical calculation involved from being made routine in the analyses of experimental results. We have developed a simulated annealing-based computational technique for routinizing the task of constrained minimization of energy functionals governing whole, or small patches of whole, fluid membranes with axisymmetry, spherical topology, and no domains of inhomogeneity. In this article, we describe the essential principles of the technique and apply it to five examples to demonstrate its versatility. It gives membrane shapes that are automatically stable to axisymmetric perturbations. Presently, it can account for constraints on 1), the membrane area or the effective membrane tension; 2), the enclosed volume or the effective pressure difference across the membrane thickness; and 3), the axial end-to-end distance or the applied axial point force.

Septin-mediated uniform bracing of phospholipid membranes

Cell shape is determined by the interplay between the lipid bilayer and the underlying network of protein polymers. We explored unknown determinants involved in cell morphogenesis as factors that transform phospholipid-based liposomes (diameter 5-20 microm). Unlabeled giant liposomes, observed through dark-field optics, were metastable in an aqueous suspension. In contrast, liposomes robustly protruded uniform tubules immediately after the addition of a brain extract to the suspension. The tubulation reaction was greatly facilitated when the liposomes contained PIP or PIP2. Biochemical analysis of the brain extract revealed that heteromeric complexes of septins, a family of polymerizing GTP/GDP-binding proteins, are responsible for the membrane transformation. Ultrastructural analysis established that each membrane tubule (diameter 0.43 +/- 0.079 microm) is braced by a circumferential array of septin filaments. Although submembranous septin assemblies are associated with diverse cortical morphogenesis from yeast to mammals, the biophysical basis for the septin-membrane interplay remains largely unknown. Further, there is a biochemical discrepancy between the fast septin remodeling in cells and their slow self-assembly in vitro. This membrane-facilitated fast septin assembly demonstrated for the first time by our unique experimental system should provide important clues to characterize these processes.

Interaction of lipopolysaccharide and phospholipid in mixed membranes: solid-state 31P-NMR spectroscopic and microscopic investigations

Lipopolysaccharide (LPS), which constitutes the outermost layer of gram-negative bacterial cells as a typical component essential for their life, induces the first line defense system of innate immunity of higher animals. To understand the basic mode of interaction between bacterial LPS and phospholipid cell membranes, distribution patterns were studied by various physical methods of deep rough mutant LPS (ReLPS) of Escherichia coli incorporated in phospholipid bilayers as simple models of cell membranes. Solid-state (31)P-NMR spectroscopic analysis suggested that a substantial part of ReLPS is incorporated into 1,2-dimyristoyl-sn-glycero-3-phosphocholine lipid bilayers when multilamellar vesicles were prepared from mixtures of these. In egg L-alpha-phosphatidylcholine (egg-PC)-rich membranes, ReLPS undergoes micellization. In phosphatidylethanolamine-rich membranes, however, micellization was not observed. We studied by microscopic techniques the location of ReLPS in membranes of ReLPS/egg-PC (1:10 M/M) and ReLPS/egg-PC/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) (1:9:1 M/M/M). The influence of ReLPS on the physicochemical properties of the membranes was studied as well. Microscopic images of both giant unilamellar vesicles and supported planar lipid bilayers showed that LPS was uniformly incorporated in the egg-PC lipid bilayers. In the egg-PC/POPG (9:1 M/M) lipid bilayers, however, ReLPS is only partially incorporated and becomes a part of the membrane in a form of aggregates (or as mixed aggregates with the lipids) on the bilayer surface. The lipid lateral diffusion coefficient measurements at various molar ratios of ReLPS/egg-PC/POPG indicated that the incorporated ReLPS reduces the diffusion coefficients of the phospholipids in the membrane. The retardation of diffusion became more significant with increasing POPG concentrations in the membrane at high ReLPS/phospholipid ratios. This work demonstrated that the phospholipid composition has critical influence on the distribution of added ReLPS in the respective lipid membranes and also on the morphology and physicochemical property of the resulting membranes. A putative major factor causing these phenomena is reasoned to be the miscibility between ReLPS and individual phospholipid compositions.

Lipid bilayer discs and banded tubules: photoinduced lipid sorting in ternary mixtures

The self-assembly of biological amphiphiles has proved a fascinating topic in recent years, the hollow cylindrical lipid tubule morphology being of particular interest due to its potential applications in "soft" microtechnologies. Lateral coexistence of liquid-ordered (lo) and liquid-disordered (ld) phases, which may resemble raft formation in cell membranes, was investigated in lipid tubules, prepared from 1,2-dioleoyl-sn-glycero-3-phosphocholine, egg-sphingomyelin, and cholesterol. Fluorescence microscopy shows that the appearance of micrometer-scale lo domains in the lipid tubule is not an intrinsic phase behavior of the system but a consequence of photoinduced lipid peroxidation. Most interestingly, new photoinduced bilayer structures: lipid discs, essentially stable flattened liposomes, were observed for the first time in a model membrane system. This investigation not only aids in our understanding of lipid sorting phenomena in cell membranes but also demonstrates how control of this process may provide a route to the generation of new, functional structures.

The effect of cellular cholesterol on membrane-cytoskeleton adhesion

Whereas recent studies suggest that cholesterol plays important role in the regulation of membrane proteins, its effect on the interaction of the cell membrane with the underlying cytoskeleton is not well understood. Here, we investigated this by measuring the forces needed to extract nanotubes (tethers) from the plasma membrane, using atomic force microscopy. The magnitude of these forces provided a direct measure of cell stiffness, cell membrane effective surface viscosity and association with the underlying cytoskeleton. Furthermore, we measured the lateral diffusion constant of a lipid analog DiIC12, using fluorescence recovery after photobleaching, which offers additional information on the organization of the membrane. We found that cholesterol depletion significantly increased the adhesion energy between the membrane and the cytoskeleton and decreased the membrane diffusion constant. An increase in cellular cholesterol to a level higher than that in control cells led to a decrease in the adhesion energy and the membrane surface viscosity. Disassembly of the actin network abrogated all the observed effects, suggesting that cholesterol affects the mechanical properties of a cell through the underlying cytoskeleton. The results of these quantitative studies may help to better understand the biomechanical processes accompanying the development of atherosclerosis.

Eukaryotic membrane tethers revisited using magnetic tweezers

Membrane nanotubes, under physiological conditions, typically form en masse. We employed magnetic tweezers (MTW) to extract tethers from human brain tumor cells and compared their biophysical properties with tethers extracted after disruption of the cytoskeleton and from a strongly differing cell type, Chinese hamster ovary cells. In this method, the constant force produced with the MTW is transduced to cells through super-paramagnetic beads attached to the cell membrane. Multiple sudden jumps in bead velocity were manifest in the recorded bead displacement-time profiles. These discrete events were interpreted as successive ruptures of individual tethers. Observation with scanning electron microscopy supported the simultaneous existence of multiple tethers. The physical characteristics, in particular, the number and viscoelastic properties of the extracted tethers were determined from the analytic fit to bead trajectories, provided by a standard model of viscoelasticity. Comparison of tethers formed with MTW and atomic force microscopy (AFM), a technique where the cantilever-force transducer is moved at constant velocity, revealed significant differences in the two methods of tether formation. Our findings imply that extreme care must be used to interpret the outcome of tether pulling experiments performed with single molecular techniques (MTW, AFM, optical tweezers, etc). First, the different methods may be testing distinct membrane structures with distinct properties. Second, as soon as a true cell membrane (as opposed to that of a vesicle) can attach to a substrate, upon pulling on it, multiple nonspecific membrane tethers may be generated. Therefore, under physiological conditions, distinguishing between tethers formed through specific and nonspecific interactions is highly nontrivial if at all possible.

Opening of holes in liposomal membranes is induced by proteins possessing the FERM domain

The destabilization of vesicles caused by interactions between lipid bilayers and proteins was studied by direct, real-time observation using high-intensity dark-field microscopy. We previously reported that talin, a cytoskeletal submembranous protein, can reversibly open stable large holes in giant liposomes made of neutral and acidic phospholipids. Talin and other proteins belonging to the band 4.1 superfamily have the FERM domain at their N-terminal and interact with lipid membranes via that domain. Here, we observed that band 4.1, ezrin and moesin, members of the band 4.1 superfamily, are also able to open stable holes in liposomes. However, truncation of their C-terminal domains, which can interact with the N-terminal FERM domain, impaired their hole opening activities. Oligomeric states of ezrin affected the capability of the membrane hole formation. Phosphatidylinositol bisphosphate (PIP2), which binds to the FERM domain and disrupts the interaction between the N and C termini of the band 4.1 superfamily, down-regulates their membrane opening activity. These results suggest that the intermolecular interaction plays a key role in the observed membrane hole formation.