Membrane Curvature Research Articles

Regulation of PIEZO1 channels by lipids and the structural components of extracellular matrix/cell cytoskeleton.

PIEZO1 is a mechanosensitive channel widely presented in eukaryotic organisms. Although the PIEZO family was discovered in 2010, main questions related to the molecular structure as well as to specific activation mechanisms and regulating pathways remain open. Two hypotheses of PIEZO1 gating were formulated: the first, as a dominant hypothesis, through the plasma membrane (force-from-lipids) and the second, via the participation of the cytoskeleton and the components of the extracellular matrix (ECM) (force-from-filaments). Many researchers provide convincing evidence for both hypotheses. It was demonstrated that PIEZO1 has a propeller-like shape forming a membrane curvature within the lipid bilayer. That suggests the participation of lipids in channel modulation, and many studies demonstrate the critical role of lipids and compounds that modify the lipid bilayer in the regulation of PIEZO1 properties. At the same time, the components of ECM and cortical cytoskeleton can be affected by the membrane curvature and thus have an impact on PIEZO1 properties. In living cells, PIEZO1 properties are reported to be critically dependent on channel microenvironment that is on combinatorial influence of plasma membrane, cytoskeleton and ECM. Thus, it is necessary to understand which factors can affect PIEZO1 and consider them when interpreting the role of PIEZO1 in various physiological processes. This review summarizes the current knowledge about regulation of Piezo1 by lipids and the components of ECM and cytoskeleton.

Structural basis of mitochondrial membrane bending by the I–II–III2–IV2 supercomplex

Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane1. Here we show that a supercomplex containing all four respiratory chain components contributes to membrane curvature induction in ciliates. We report cryo-electron microscopy and cryo-tomography structures of the supercomplex that comprises 150 different proteins and 311 bound lipids, forming a stable 5.8-MDa assembly. Owing to subunit acquisition and extension, complex I associates with a complex IV dimer, generating a wedge-shaped gap that serves as a binding site for complex II. Together with a tilted complex III dimer association, it results in a curved membrane region. Using molecular dynamics simulations, we demonstrate that the divergent supercomplex actively contributes to the membrane curvature induction and tubulation of cristae. Our findings highlight how the evolution of protein subunits of respiratory complexes has led to the I–II–III2–IV2 supercomplex that contributes to the shaping of the bioenergetic membrane, thereby enabling its functional specialization.

Physics-based generative model of curvature sensing peptides; distinguishing sensors from binders.

Proteins can specifically bind to curved membranes through curvature-induced hydrophobic lipid packing defects. The chemical diversity among such curvature "sensors" challenges our understanding of how they differ from general membrane "binders" that bind without curvature selectivity. Here, we combine an evolutionary algorithm with coarse-grained molecular dynamics simulations (Evo-MD) to resolve the peptide sequences that optimally recognize the curvature of lipid membranes. We subsequently demonstrate how a synergy between Evo-MD and a neural network (NN) can enhance the identification and discovery of curvature sensing peptides and proteins. To this aim, we benchmark a physics-trained NN model against experimental data and show that we can correctly identify known sensors and binders. We illustrate that sensing and binding are phenomena that lie on the same thermodynamic continuum, with only subtle but explainable differences in membrane binding free energy, consistent with the serendipitous discovery of sensors.

Mechanistic analysis of a novel membrane-interacting variable loop in the pleckstrin-homology domain critical for dynamin function

Classical dynamins are best understood for their ability to generate vesicles by membrane fission. During clathrin-mediated endocytosis (CME), dynamin is recruited to the membrane through multivalent protein and lipid interactions between its proline-rich domain (PRD) with SRC Homology 3 (SH3) domains in endocytic proteins and its pleckstrin-homology domain (PHD) with membrane lipids. Variable loops (VL) in the PHD bind lipids and partially insert into the membrane thereby anchoring the PHD to the membrane. Recent molecular dynamics (MD) simulations reveal a novel VL4 that interacts with the membrane. Importantly, a missense mutation that reduces VL4 hydrophobicity is linked to an autosomal dominant form of Charcot-Marie-Tooth (CMT) neuropathy. We analyzed the orientation and function of the VL4 to mechanistically link data from simulations with the CMT neuropathy. Structural modeling of PHDs in the cryo-electron microscopy (cryo-EM) cryoEM map of the membrane-bound dynamin polymer confirms VL4 as a membrane-interacting loop. In assays that rely solely on lipid-based membrane recruitment, VL4 mutants with reduced hydrophobicity showed an acute membrane curvature-dependent binding and a catalytic defect in fission. Remarkably, in assays that mimic a physiological multivalent lipid- and protein-based recruitment, VL4 mutants were completely defective in fission across a range of membrane curvatures. Importantly, expression of these mutants in cells inhibited CME, consistent with the autosomal dominant phenotype associated with the CMT neuropathy. Together, our results emphasize the significance of finely tuned lipid and protein interactions for efficient dynamin function.

Activity and Structural Dynamics of Human ABCA1 in a Lipid Membrane

The human ATP-binding cassette (ABC) transporter ABCA1 plays a critical role in lipid homeostasis as it extracts sterols and phospholipids from the plasma membrane for excretion to the extracellular apolipoprotein A-I and subsequent formation of high-density lipoprotein (HDL) particles. Deleterious mutations of ABCA1 lead to sterol accumulation and are associated with atherosclerosis, poor cardiovascular outcomes, cancer, and Alzheimer’s disease. The mechanism by which ABCA1 drives lipid movement is poorly understood, and a unified platform to produce active ABCA1 protein for both functional and structural studies has been missing. In this work, we established a stable expression system for both a human cell-based sterol export assay and protein purification for in vitro biochemical and structural studies. ABCA1 produced in this system was active in sterol export and displayed enhanced ATPase activity after reconstitution into a lipid bilayer. Our single-particle cryo-EM study of ABCA1 in nanodiscs showed protein induced membrane curvature, revealed multiple distinct conformations, and generated a structure of nanodisc-embedded ABCA1 at 4.0-Å resolution representing a previously unknown conformation. Comparison of different ABCA1 structures and molecular dynamics simulations demonstrates both concerted domain movements and conformational variations within each domain. Taken together, our platform for producing and characterizing ABCA1 in a lipid membrane enabled us to gain important mechanistic and structural insights and paves the way for investigating modulators that target the functions of ABCA1.

Morphofunctional changes at the active zone during synaptic vesicle exocytosis

Synaptic vesicle (SV) fusion with the plasma membrane (PM) proceeds through intermediate steps that remain poorly resolved. The effect of persistent high or low exocytosis activity on intermediate steps remains unknown. Using spray‐mixing plunge‐freezing cryo‐electron tomography we observe events following synaptic stimulation at nanometer resolution in near‐native samples. Our data suggest that during the stage that immediately follows stimulation, termed early fusion, PM and SV membrane curvature changes to establish a point contact. The next stage—late fusion—shows fusion pore opening and SV collapse. During early fusion, proximal tethered SVs form additional tethers with the PM and increase the inter‐SV connector number. In the late‐fusion stage, PM‐proximal SVs lose their interconnections, allowing them to move toward the PM. Two SNAP‐25 mutations, one arresting and one disinhibiting spontaneous release, cause connector loss. The disinhibiting mutation causes loss of membrane‐proximal multiple‐tethered SVs. Overall, tether formation and connector dissolution are triggered by stimulation and respond to spontaneous fusion rate manipulation. These morphological observations likely correspond to SV transition from one functional pool to another.

Actin-rich lamellipodia-like protrusions contribute to the integrity of epithelial cell–cell junctions

Metastasis-suppressor 1 (MTSS1) is a membrane-interacting scaffolding protein that regulates the integrity of epithelial cell-cell junctions and functions as a tumor suppressor in a wide range of carcinomas. MTSS1 binds phosphoinositide-rich membranes through its I-BAR domain and is capable of sensing and generating negative membrane curvature invitro. However, the mechanisms by which MTSS1 localizes to intercellular junctions in epithelial cells and contributes to their integrity and maintenance have remained elusive. By carrying out EM and live-cell imaging on cultured Madin-Darby canine kidney cell monolayers, we provide evidence that adherens junctions of epithelial cells harbor lamellipodia-like, dynamic actin-driven membrane folds, which exhibit high negative membrane curvature at their distal edges. BioID proteomics and imaging experiments demonstrated that MTSS1 associates with an Arp2/3 complex activator, the WAVE-2 complex, in dynamic actin-rich protrusions at cell-cell junctions. Inhibition of Arp2/3 or WAVE-2 suppressed actin filament assembly at adherens junctions, decreased the dynamics of junctional membrane protrusions, and led to defects in epithelial integrity. Together, these results support a model in which membrane-associated MTSS1, together with the WAVE-2 and Arp2/3 complexes, promotes the formation of dynamic lamellipodia-like actin protrusions that contribute to the integrity of cell-cell junctions in epithelial monolayers.

Cyclic lipopeptides as membrane fusion inhibitors against SARS-CoV-2: New tricks for old dogs

With the resurgence of the coronavirus pandemic, the repositioning of FDA-approved drugs against coronovirus and finding alternative strategies for antiviral therapy are both important. We previously identified the viral lipid envelope as a potential target for the prevention and treatment of SARS-CoV-2 infection with plant alkaloids (Shekunov et al., 2021). Here, we investigated the effects of eleven cyclic lipopeptides (CLPs), including well-known antifungal and antibacterial compounds, on the liposome fusion triggered by calcium, polyethylene glycol 8000, and a fragment of SARS-CoV-2 fusion peptide (816–827) by calcein release assays. Differential scanning microcalorimetry of the gel-to-liquid-crystalline and lamellar-to-inverted hexagonal phase transitions and confocal fluorescence microscopy demonstrated the relation of the fusion inhibitory effects of CLPs to alterations in lipid packing, membrane curvature stress and domain organization. The antiviral effects of CLPs were evaluated in an in vitro Vero-based cell model, and aculeacin A, anidulafugin, iturin A, and mycosubtilin attenuated the cytopathogenicity of SARS-CoV-2 without specific toxicity.

The effect of tailing lipidation on the bioactivity of antimicrobial peptides and their aggregation tendency

AbstractAntimicrobial peptides (AMPs) are potentially powerful alternatives to conventional antibiotics in combating multidrug resistance, given their broad spectrum of activity. They mainly interact with cell membranes through surface electrostatic potentials and the formation of secondary structures, resulting in permeability and destruction of target microorganism membranes. Our earlier work showed that two leading AMPs, MSI‐78 (4–20) and pardaxin (1–22), had potent antimicrobial activity against a range of bacteria. It is known that the attachment of moderate‐length lipid carbon chains to cationic peptides can further improve the functionality of these peptides through enhanced interactions with the membrane lipid bilayer, inducing membrane curvature, destabilization, and potential leakage. Thus, in this work, we aimed to investigate the antimicrobial activity, oligomerization propensity, and lipid‐membrane binding interactions of a range of N‐terminal lipidated analogs of MSI‐78 (4–20) and pardaxin (1–22). Molecular modeling results suggest that aggregation of the N‐lipidated AMPs may impart greater structural stability to the peptides in solution and a greater depth of lipid bilayer insertion for the N‐lipidated AMPs over the parental peptide. Our experimental and computational findings provide insights into how N‐terminal lipidation of AMPs may alter their conformations, with subsequent effects on their functional properties in regard to their self‐aggregation behavior, membrane interactions, and antimicrobial activity.

Morphological Behavior of Liposomes and Lipid Nanoparticles.

Liposomes, which consist of bilayer lipids surrounding interior aqueous compartment(s), were first characterized nearly 60 years ago. Remarkably, many fundamental properties of liposomes and their micellar-like "solid core" counterparts (a lipid monolayer surrounding a hydrophobic core) and transitions between these structures remain poorly understood. In this work, we examine the effects of basic variables on the morphology adopted by lipid-based systems produced by rapid mixing of lipids in ethanol with aqueous media. We show that, for lipids such as distearolyphosphatidylcholine (DSPC)-cholesterol mixtures that form bilayer vesicles on hydration, osmotic stress can induce regions of high positive membrane curvature, leading to fusion between unilamellar vesicles to produce bilamellar vesicles. Addition of lyso PC, an "inverted cone"-shaped lipid that supports regions of high positive curvature, can inhibit the formation of these bilamellar vesicles by stabilizing a hemifused intermediate structure. Conversely, the presence of "cone"-shaped lipids such as dioleoylphosphatidylethanolamine (DOPE) that results in negative membrane curvature promotes fusion events subsequent to vesicle formation (during the ethanol dialysis stage), leading to bilamellar and multilamellar systems even in the absence of osmotic stress. Alternatively, the presence of increasing amounts of triolein, a lipid that is insoluble in lipid bilayers, results in increasing internal solid core structures until micellar-like systems with a hydrophobic core of triolein are achieved. These results are interpreted in terms of the intrinsic membrane curvature that bilayer vesicles can stably maintain as well as the ability of bilayer lipids to first form a monolayer around a solid core of hydrophobic material such as triolein and then, as the proportion of bilayer lipids is increased, progressively form bilayer structures that can eventually form a complete bilayer encapsulating both a hydrophobic core and an aqueous compartment. These hybrid intermediate structures may have utility as novel drug delivery systems.

Branched actin cortices reconstituted in vesicles sense membrane curvature

The actin cortex is a complex cytoskeletal machinery that drives and responds to changes in cell shape. It must generate or adapt to plasma membrane curvature to facilitate diverse functions such as cell division, migration, and phagocytosis. Due to the complex molecular makeup of the actin cortex, it remains unclear whether actin networks are inherently able to sense and generate membrane curvature, or whether they rely on their diverse binding partners to accomplish this. Here, we show that curvature sensing is an inherent capability of branched actin networks nucleated by Arp2/3 and VCA. We develop a robust method to encapsulate actin inside giant unilamellar vesicles (GUVs) and assemble an actin cortex at the inner surface of the GUV membrane. We show that actin forms a uniform and thin cortical layer when present at high concentration and distinct patches associated with negative membrane curvature at low concentration. Serendipitously, we find that the GUV production method also produces dumbbell-shaped GUVs, which we explain using mathematical modeling in terms of membrane hemifusion of nested GUVs. We find that branched actin networks preferentially assemble at the neck of the dumbbells, which possess a micrometer-range convex curvature comparable with the curvature of the actin patches found in spherical GUVs. Minimal branched actin networks can thus sense membrane curvature, which may help mammalian cells to robustly recruit actin to curved membranes to facilitate diverse cellular functions such as cytokinesis and migration.

Disease-associated mutations in Drp1 have fundamentally different effects on the mitochondrial fission machinery.

Patient mutations have been identified throughout dynamin-related protein 1 (Drp1), the key protein mediator of mitochondrial fission. These changes generally impact young children and often result in severe neurological defects and, in some instances, death. Until now, the underlying functional defect leading to patient phenotypes has been largely speculative. We therefore analyzed six disease-associated mutations throughout the GTPase and middle domains (MD) of Drp1. The MD plays a role in Drp1 oligomerization, and three mutations in this region were predictably impaired in self-assembly. However, another mutant in this region (F370C) retained oligomerization capability on pre-curved membranes despite being assembly-limited in solution. Instead, this mutation impaired membrane remodeling of liposomes, which highlights the importance of Drp1 in generating local membrane curvature before fission. Two GTPase domain mutations were also observed in different patients. The G32A mutation was impaired in GTP hydrolysis both in solution and in the presence of lipid but remains capable of self-assembly on these lipid templates. The G223V mutation also exhibited decreased GTPase activity and was able to assemble on pre-curved lipid templates; however, this change impaired membrane remodeling of unilamellar liposomes similar to F370C. This demonstrates that the Drp1 GTPase domain also contributes to self-assembly interactions that drive membrane curvature. Overall, the functional defects caused by mutations in Drp1 are highly variable even for mutations that reside within the same functional domain. This study provides a framework for characterizing additional Drp1 mutations to provide a comprehensive understanding of functional sites within this essential protein.

Get in and get out: Remodeling of the cellular actin cytoskeleton upon HIV-1 infection.

The human immunodeficiency virus type 1 (HIV-1) is an intracellular pathogen whose replication cycle strictly depends on the host cell molecular machinery. HIV-1 crosses twice the plasma membrane, to get in and to get out of the cell. Therefore, the first and the last line of intracellular component encountered by the virus is the cortical actin network. Here, we review the role of actin and actin-related proteins in HIV-1 entry, assembly, budding, and release. We first highlight the mechanisms controlling actin polymerization at the entry site that promote the clustering of HIV-1 receptors, a crucial step for the virus to fuse with the plasma membrane. Then, we describe how actin is transiently depolymerized locally to allow the capsid to cross the actin cortex, before migrating towards the nucleus. Finally, we review the role of several actin-binding proteins in actin remodeling events required for membrane deformation and curvature at the viral assembly site as well as for virus release. Strikingly, it appears that common actin-regulating pathways are involved in viral entry and exit. However, while the role of actin remodeling during entry is well understood, this is not the case during exit. We discuss remaining challenges regarding the actin-dependent mechanisms involved in HIV-1 entry and exit, and how they could be overcome.

Molecular mechanism of GTP binding- and dimerization-induced enhancement of Sar1-mediated membrane remodeling

The Sar1 GTPase initiates coat protein II (COPII)-mediated protein transport by generating membrane curvature at subdomains on the endoplasmic reticulum, where it is activated by the guanine nucleotide exchange factor (GEF) Sec12. Crystal structures of GDP- and GTP-bound forms of Sar1 suggest that it undergoes a conformational switch in which GTP binding enhances the exposure of an amino-terminal amphipathic helix necessary for efficient membrane penetration. However, key residues in the amino terminus were not resolved in crystal structures, and experimental studies have suggested that the amino terminus of Sar1 is solvent-exposed in the absence of a membrane, even in the GDP-bound state. Therefore, the molecular mechanism by which GTP binding activates the membrane-remodeling activity of Sar1 remains unclear. Using atomistic molecular dynamics simulations, we compare the membrane-binding and curvature generation activities of Sar1 in its GDP- and GTP-bound states. We show that in the GTP-bound state, Sar1 inserts into the membrane with its complete (residues 1 to 23) amphipathic amino-terminal helix, while Sar1-GDP binds to the membrane only through its first 12 residues. Such differential membrane-binding modes translate into significant differences in the protein volume inserted into the membrane. As a result, Sar1-GTP generates positive membrane curvature 10 to 20 times higher than Sar1-GDP. Dimerization of the GTP-bound form of Sar1 further amplifies curvature generation. Taken together, our results present a detailed molecular mechanism for how the nucleotide-bound state of Sar1 regulates its membrane-binding and remodeling activities in a concentration-dependent manner, paving the way toward a better understanding COPII-mediated membrane transport.

Phospholipases and Membrane Curvature: What Is Happening at the Surface?

In this revision work, we emphasize the close relationship between the action of phospholipases and the modulation of membrane curvature and curvature stress resulting from this activity. The alteration of the tridimensional structure of membranes upon the action of phospholipases is analyzed based on studies on model lipid membranes. The transient unbalance of both compositional and physical membrane properties between the hemilayers upon phospholipase activity lead to curvature tension and the catalysis of several membrane-related processes. Several proteins' membrane-bound and soluble forms are susceptible to regulation by the curvature stress induced by phospholipase action, which has important consequences in cell signaling. Additionally, the modulation of membrane fusion by phospholipase products regulates membrane dynamics in several cellular scenarios. We commented on vesicle fusion in the Golgi-endoplasmic system, synaptic vesicle fusion to the plasma membrane, viral membrane fusion to host cell plasma membrane and gametes membrane fusion upon acrosomal reaction. Furthermore, we explored the modulation of membrane fusion by the asymmetric adsorption of amphiphilic drugs. A deep understanding of the relevance of lipid membrane structure, particularly membrane curvature and curvature stress, on different cellular events leads to the challenge of its regulation, which may become a powerful tool for pharmacological therapy.

Membrane mechanics regulate the cooperativity of proteins in curvature sensing.

Recruitment of proteins to a membrane surface is critical for many biological processes, such as clathrin-mediated endocytosis and signaling. When interacting with the lipid membrane, many proteins exhibit different affinities to membranes with different curvature, known as curvature sensing. They also generate membrane curvature (curvature induction) by a variety of mechanisms, including the insertion of amphipathic helices. Here we use a continuum membrane model to study how helix insertions can alter the membrane energetics and how the mechanical feedback of the membrane regulates the helix insertions. Our membrane model has two coupled layers of triangular mesh to represent the two monolayers of the bilayer membrane, capturing membrane thickness and tilt. We analyzed the membrane deformation around one helix insertion and compared it to molecular dynamic simulations to optimally define the lipid tilt energies. We then investigate the interactions between insertions and membranes by considering the copy number of insertions and their interval distance, membrane tension or stress before the insertions, membrane curvatures, and lipid composition. Our results showed that multiple insertions exhibit a mechanism of cooperativity; each binding event is not independent of previous events. Our results show that this cooperativity is dependent on membrane tension and curvature. In comparison to experimental data, we validated our simulation results and analyzed the role of lipid flip-flop across the bilayers. Quantifying how protein and membrane interactions feedback on one another is critical for understanding the dynamics and control of proteins that remodel membranes through localization and self-assembly in various cellular processes.

Modeling the mechanisms through which protein phase separation induces membrane curvature.

Membrane curvature is an essential component of life. Many cellular processes, such as endocytosis, exocytosis, and cell motility induce curvature in membranes to carry out their functions. Though it is traditionally thought that structured proteins drive curvature, recent work has shown that disordered proteins can also be potent drivers of curvature. In particular, liquid-like condensation of disordered proteins has recently been shown to produce concave membrane curvature, resulting in protein-lined buds and tubules of the membrane. However, the mechanism behind this phenomenon remains poorly understood. Here we seek to understand the protein-protein and protein-membrane interactions that give rise to these behaviors. We begin by using coarse grained molecular dynamics simulations to investigate the conformational preferences of disordered proteins under different conditions: in varying salt concentrations, in solution or tethered to a lipid membrane. Specifically, we examine the deviation of disordered protein behavior from that of a simple random walk, both in solution and on membrane surfaces. By comparing modeling results to experimental data, we separate the role of protein-protein and protein-membrane interactions to shed light on the role of each in both phase separation and curvature generation. Our work will provide insight on the role that disordered regions have in membrane complexes, particularly those which facilitate membrane curvature.

Membrane curvature regulates the spatial distribution of bulky glycoproteins.

The glycocalyx is a shell of heavily glycosylated proteins and lipids distributed on the cell surface of nearly all cell types. Recently, it has been found that bulky transmembrane glycoproteins such as MUC1 can modulate membrane shape by inducing membrane protrusions. In this work, we examine the reciprocal relationship of how membrane shape affects MUC1's spatial distribution on the cell membrane and its biological significance. By employing nanopatterned surfaces and membrane-sculpting proteins to manipulate membrane curvature, we show that MUC1 avoids positively-curved membranes (membrane invaginations) and accumulates on negatively-curved membranes (membrane protrusions). MUC1's curvature sensitivity is dependent on the length and the extent of glycosylation of its ectodomain, with large and highly glycosylated forms preferentially staying out of positive curvature. Interestingly, MUC1's avoidance of positive membrane curvature enables it to escape from endocytosis and being removed from the cell membrane. These findings also suggest that the truncation of MUC1's ectodomain, often observed in breast and ovarian cancers, may enhance its endocytosis and potentiate its intracellular accumulation and signaling.

Using quantitative microscopy approaches to study the formation of clathrin-coated vesicles.

Clathrin-coated vesicles (CCVs) are endocytic carriers that mediate the internalization of ligands and their receptors from the plasma membrane. CCVs assembly requires the coordinated recruitment of many proteins that promote receptor sorting and membrane curvature formation. Clathrin triskelia together with the adaptors AP2 and clathrin assembly lymphoid myeloid leukemia protein (CALM) are the most represented components of CCVs. CALM supports the formation of membrane curvature that is essential for the growth of CCVs. Membrane curvature can be reached only by overcoming local plasma membrane tension that, together with the availability of CCV components, determines the type of clathrin structures that forms over the plasma membrane. We hypothesized that CALM recruitment could support the formation of CCVs even under mechanically stringent conditions, such as increased membrane tension. To investigate this, we used knock-in gene editing to obtain cells expressing fluorescently tagged CALM at endogenous levels and spinning-disc and lattice light sheet live-cell microscopy calibrated to the intensity of a single molecule to quantitatively study CALM recruitment during the formation of CCVs in normal conditions, upon membrane tension increase, and/or CALM depletion. Our results demonstrate that CALM promotes CCV completion under membrane tension increase possibly by a mechanism based on protein-protein crowding at the neck of the CCV. We also observed that CALM is differentially expressed across cell types and that given the small footprint of CALM, there is sufficient room on the CCV surface to recruit CALM molecules as needed, depending on the local membrane tension and cellular availability. In conclusion, our data suggest that the competence in clathrin-mediated endocytosis differs across cells and tissues and explain the reason why CALM is essential during embryo development but dispensable in other cellular contexts.

Membrane curvature sensed and induced by formin binding Protein 17.

Cell functions such as motility, differentiation, protein trafficking or signal transduction, often require some membrane reshaping events involving a change in membrane curvature and protein distribution. Defects associated with the proteins involved in membrane reshaping can cause several diseases such as centronuclear myopathy or Charcot-Marie-Tooth neuropathies. Among the proteins associated with alteration in membrane curvature, BAR (Bin/Amphiphysin/Rvs) domain proteins stand out. BAR domain proteins are crescent shaped dimeric structures that bind to lipid bilayers through electrostatic interactions. These curvature sensitive proteins are capable of inducing both local and global curvatures. However, the complexity of the mechanisms of the interactions between these proteins and lipid bilayers are not well known. Computational studies of these protein-membrane interactions using molecular dynamics are often coarse-grained as opposed to all-atoms simulations. In the present study, we explore the curvature sensitivity and inducing properties of Formin Binding Protein 17 (fbp17) through all-atoms molecular dynamics simulations. We simulated fbp17 with different lipid bilayer compositions on flat and buckled bilayers. We were able to isolate the residues involved in the interactions. Our results suggest that fbp17 can induce a certain range of local curvature on various flat membranes. Fp17 can also sense or conform to various ranges of curved bilayers. These results give an insight into the role of BAR domain protein in general, and fbp17 in particular in the context of membrane structural fluctuations.