Biophysical Properties Of Plasma Membrane Research Articles

A fatty acid elongase complex regulates cell membrane integrity and septin-dependent host infection by the rice blast fungus.

Very-long-chain fatty acids (VLCFAs) regulate biophysical properties of cell membranes to determine growth and development of eukaryotes, such as the pathogenesis of the rice blast fungus Magnaporthe oryzae. The fatty acid elongase Elo1 regulates pathogenesis of M. oryzae by modulating VLCFA biosynthesis. However, it remains unknown whether and how Elo1 associates with other factors to regulate VLCFA biosynthesis in fungal pathogens. Here, we identified Ifa38, Phs1 and Tsc13 as interacting proteins of Elo1 by proximity labelling in M. oryzae. Elo1 associated with Ifa38, Phs1 and Tsc13 on the endoplasmic reticulum (ER) membrane to control VLCFA biosynthesis. Targeted gene deletion mutants Δifa38, Δphs1 and Δtsc13 were all similarly impaired as Δelo1 in vegetative growth, conidial morphology, stress responses in ER, cell wall and membrane. These deletion mutants also displayed severe damage in cell membrane integrity and failed to organize the septin ring that is essential for penetration peg formation and pathogenicity. Our study demonstrates that M. oryzae employs a fatty acid elongase complex to regulate VLCFAs for maintaining or remodelling cell membrane structure, which is important for septin-mediated host penetration.

Dietary (poly)phenols as modulators of the biophysical properties in endothelial cell membranes: its impact on nitric oxide bioavailability in hypertension.

Hypertension is a major contributor to premature death, owing to the associated increased risk of damage to the heart, brain and kidneys. Although hypertension is manageable by medication and lifestyle changes, the risk increases with age. In an increasingly aged society, the incidence of hypertension is escalating, and is expected to increase the prevalence of (cerebro)vascular events and their associated mortality. Adherence to plant-based diets improves blood pressure and vascular markers in individuals with hypertension. Food flavonoids have an inhibitory effect towards angiotensin-converting enzyme (ACE1) and although this effect is greatly diminished upon metabolization, their microbial metabolites have been found to improve endothelial nitric oxide synthase (eNOS) activity. Considering the transmembrane location of ACE1 and eNOS, the ability of (poly)phenols to interact with membrane lipids modulate the cell membrane's biophysical properties and impact on nitric oxide (·NO) synthesis and bioavailability, remain poorly studied. Herein, we provide an overview of the current knowledge on the lipid remodeling of endothelial membranes with age, its impact on the cell membrane's biophysical properties and ·NO permeability across the endothelial barrier. We also discuss the potential of (poly)phenols and other plant-based compounds as key players in hypertension management, and address the caveats and challenges in adopted methodologies.

Surface nanoroughness impacts the formation and stability of supported lipid bilayers

Solid supported lipid bilayers (SLBs) are excellent platforms for studying the biophysical properties of cell membranes, as well as versatile biomimetic films for biotechnology applications. Among the existing approaches used to form SLBs, vesicle fusion and rupture onto solid supports is the most commonly employed one owing to its straightforward procedure. SLBs are typically formed on atomically flat and very hydrophilic surfaces, overlooking the influence of roughness and topography on membrane formation and organization. As a matter of fact, lipid bilayers in vivo are corrugated at the nanoscale level, as a result of interactions with proteins, fibrils, and other components within the intracellular and extracellular environment. Fundamental studies of the effect of surface roughness on SLBs are scarce and restricted to few contributions, where nanoroughness has shown to affect lipid mobility by a 5-fold decrease and inhibit domain growth in phase-separated membranes. In this work, the impact of nanoroughness on the formation and stability of SLBs onto SiO2 surfaces with different degrees of vertical and lateral surface roughness is studied. Combining quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy with force spectroscopy (AFM-FS), it is shown that nanoroughness affects the formation of SLBs by increasing the activation energy of vesicle fusion, rupture and spreading, and weakens the stability and lateral organization of the formed SLBs.

High spatial-resolved heat manipulating membrane heterogeneity alters cellular migration and signaling.

Plasma membrane heterogeneity is a key biophysical regulatory principle of membrane protein dynamics, which further influences downstream signal transduction. Although extensive biophysical and cell biology studies have proven membrane heterogeneity is essential to cell fate, the direct link between membrane heterogeneity regulation to cellular function remains unclear. Heterogeneous structures on plasma membranes, such as lipid rafts, are transiently assembled, thus hard to study via regular techniques. Indeed, it is nearly impossible to perturb membrane heterogeneity without changing plasma membrane compositions. In this study, we developed a high-spatial resolved DNA-origami-based nanoheater system with specific lipid heterogeneity targeting to manipulate the local lipid environmental temperature under near-infrared (NIR) laser illumination. Our results showed that the targeted heating of the local lipid environment influences the membrane thermodynamic properties, which further triggers an integrin-associated cell migration change. Therefore, the nanoheater system was further applied as an optimized therapeutic agent for wound healing. Our strategy provides a powerful tool to dynamically manipulate membrane heterogeneity and has the potential to explore cellular function through changes in plasma membrane biophysical properties.

Global lipid remodelling by hypoxia aggravates migratory potential in pancreatic cancer while maintaining plasma membrane homeostasis

Hypoxia plays an important role in pancreatic cancer progression. It drives various metabolic reprogramming in cells including that of lipids, which in turn, can modify the structure and function of cell membranes. Homeostatic adaptation of membranes is well-recognized, but how and if it is regulated in hypoxic pancreatic cancer and its relation to aggressive phenotype and metastasis remains elusive. Here we show hypoxia-induced extensive global lipid remodelling spanning changes in lipid classes, unsaturation levels, glyceryl backbone and acyl chain lengths. No major modulation of plasma membrane biophysical properties revealed a decoupling of lipidome modulation from membrane properties under hypoxia. This was supported by observing minor changes in the lipidome of plasma membranes under hypoxia. Further, hypoxia increased migration and invasion underpinned by reduced actin volume, cell cortical stiffness and facile tether dynamics. In conclusion, we demonstrate buffering of the lipidome alterations leading to a homeostatic membrane response. These findings will help to understand the hypoxic regulation of pancreatic membrane homeostasis and identify tangible theranostic avenues.

Biophysical Properties of Lipid Membranes from Barley Roots during Low-Temperature Exposure and Recovery.

Glycerolipid remodeling, a dynamic mechanism for plant subsistence under cold stress, has been posited to affect the biophysical properties of cell membranes. In barley roots, remodeling has been observed to take place upon exposure to chilling stress and to be partially reverted during stress relief. In this study, we explored the biophysical characteristics of membranes formed with lipids extracted from barley roots subjected to chilling stress, or during a subsequent short- or long-term recovery. Our aim was to determine to what extent barley roots were able to offset the adverse effects of temperature on their cell membranes. For this purpose, we analyzed the response of the probe Laurdan inserted in bilayers of different extracts, the zeta potential of liposomes, and the behavior of Langmuir monolayers upon compression. We found important changes in the order of water molecules, which is in agreement with the changes in the unsaturation index of lipids due to remodeling. Regarding Langmuir monolayers, we found that films from all the extracts showed a reorganization at a surface pressure that depends on temperature. This reorganization occurred with an increase in entropy for extracts from control plants and without entropy changes for extracts from acclimated plants. In summary, some membrane properties were recovered after the stress, while others were not, suggesting that the membrane biophysical properties play a role in the mechanism of plant acclimation to chilling. These findings contribute to our understanding of the impact of lipid remodeling on biophysical modifications in plant roots.

Synthetic Cell Armor Made of DNA Origami.

The bioengineering applications of cells, such as cell printing and multicellular assembly, are directly limited by cell damage and death due to a harsh environment. Improved cellular robustness thus motivates investigations into cell encapsulation, which provides essential protection. Here we target the cell-surface glycocalyx and cross-link two layers of DNA nanorods on the cellular plasma membrane to form a modular and programmable nanoshell. We show that the DNA origami nanoshell modulates the biophysical properties of cell membranes by enhancing the membrane stiffness and lowering the lipid fluidity. The nanoshell also serves as armor to protect cells and improve their viability against mechanical stress from osmotic imbalance, centrifugal forces, and fluid shear stress. Moreover, it enables mediated cell-cell interactions for effective and robust multicellular assembly. Our results demonstrate the potential of the nanoshell, not only as a cellular protection strategy but also as a platform for cell and cell membrane manipulation.

Scanning ion conductance microscopy reveals differential effect of PM2.5 exposure on A549 lung epithelial and SH-SY5Y neuroblastoma cell membranes.

Numerous studies have linked a wide range of diseases including respiratory illnesses to harmful particulate matter (PM) emissions indoors and outdoors, such as incense PM and industrial PM. Because of their ability to penetrate the lower respiratory tract and the circulatory system, fine particles with diameters of 2.5µm or less (PM2.5) are believed to be more hazardous than larger PMs. Despite the enormous number of studies focusing on the intracellular processes associated with PM2.5 exposure, there have been limited reports studying the biophysical properties of cell membranes, such as nanoscale morphological changes induced by PM2.5. Our study assesses the membrane topographical and structural effects of PM2.5 from incense PM2.5 exposure in real time on A549 lung carcinoma epithelial cells and SH-SY5Y neuroblastoma cells that had been fixed to preclude adaptive cell responses. The size distribution and mechanical properties of the PM2.5 sample were characterized with atomic force microscopy (AFM). Nanoscale morphological monitoring of the cell membranes utilizing scanning ion conductance microscopy (SICM) indicated statistically significant increasing membrane roughness at A549 cells at half an hour of exposure and visible damage at 4h of exposure. In contrast, no significant increase in roughness was observed on SH-SY5Y cells after half an hour of PM2.5 exposure, although continued exposure to PM2.5 for up to 4h affected an expansion of lesions already present before exposure commenced. These findings suggest that A549 cell membranes are more susceptible to structural damage by PM2.5 compared to SH-SY5Y cell membranes, corroborating more enhanced susceptibility of airway epithelial cells to exposure to PM2.5 than neuronal cells.

QCM‐D Study of the Formation of Solid‐Supported Artificial Lipid Membranes: State‐of‐the‐Art, Recent Advances, and Perspectives

Solid‐supported lipid bilayers (SLBs) are excellent platforms for studying the biophysical properties of cell membranes. Among the existing approaches used to form SLBs, vesicle fusion and rupture onto solid supports are most commonly employed owing to their straightforward procedure. The current understanding of the mechanisms behind this approach has greatly benefited from the use of surface‐sensitive techniques, especially quartz crystal microbalance with dissipation monitoring (QCM‐D) in combination with other analytical techniques, such as atomic force microscopy (AFM) or localized surface plasmon resonance (LSPR). Herein, an overview of the pathways of vesicle adsorption and rupture under various experimental conditions is provided. Examples including recent findings of how the variation of the properties of lipid vesicles (size, charge), aqueous buffer (pH, ionic strength, osmotic pressure), and solid support (surface energy) affect the pathway mechanism of adsorption and rupture are provided. Recent reports on poorly understood properties such as surface roughness and topography are provided, together with the need for further studies relevant to biomimetic and sensing purposes.

Sterylglucosides in Fungi.

Sterylglucosides (SGs) are sterol conjugates widely distributed in nature. Although their universal presence in all living organisms suggests the importance of this kind of glycolipids, they are yet poorly understood. The glycosylation of sterols confers a more hydrophilic character, modifying biophysical properties of cell membranes and altering immunogenicity of the cells. In fungi, SGs regulate different cell pathways to help overcome oxygen and pH challenges, as well as help to accomplish cell recycling and other membrane functions. At the same time, the level of these lipids is highly controlled, especially in wild-type fungi. In addition, modulating SGs metabolism is becoming a novel tool for vaccine and antifungal development. In the present review, we bring together multiple observations to emphasize the underestimated importance of SGs for fungal cell functions.

Aquaporin-3 and Aquaporin-5 Facilitate Migration and Cell–Cell Adhesion in Pancreatic Cancer by Modulating Cell Biomechanical Properties

Background: Aquaporins are membrane channels responsible for the bidirectional transfer of water and small non-charged solutes across cell membranes. AQP3 and AQP5 are overexpressed in pancreatic ductal adenocarcinoma, playing key roles in cell migration, proliferation, and invasion. Here, we evaluated AQP3 and AQP5 involvement in cell biomechanical properties, cell–cell adhesion, and cell migration, following a loss-of-function strategy on BxPC-3 cells. Results: Silencing of AQP3 and AQP5 was functionally validated by reduced membrane permeability and had implications on cell migration, slowing wound recovery. Moreover, silenced AQP5 and AQP3/5 cells showed higher membrane fluidity. Biomechanical and morphological changes were assessed by atomic force microscopy (AFM), revealing AQP5 and AQP3/5 silenced cells with a lower stiffness than their control. Through cell–cell adhesion measurements, the work (energy) necessary to detach two cells was found to be lower for AQP-silenced cells than control, showing that these AQPs have implications on cell–cell adhesion. Conclusion: These findings highlight AQP3 and AQP5 involvement in the biophysical properties of cell membranes, whole cell biomechanical properties, and cell–cell adhesion, thus having potential implication in the settings of tumor development.

Laurdan in live cell imaging: Effect of acquisition settings, cell culture conditions and data analysis on generalized polarization measurements.

Cell function is highly dependent on membrane structure, organization, and fluidity. Therefore, methods to probe the biophysical properties of biological membranes are required. Determination of generalized polarization (GP) values using Laurdan in fluorescence microscopy studies is one of the most widely-used methods to investigate changes in membrane fluidity in vitro and in vivo. In the last couple of decades, there has been a major increase in the number of studies using Laurdan GP, where several different methodological approaches are used. Such differences interfere with data interpretation inasmuch as it is difficult to validate if Laurdan GP variations actually reflect changes in membrane organization or arise from biased experimental approaches. To address this, we evaluated the influence of different methodological details of experimental data acquisition and analysis on Laurdan GP. Our results showed that absolute GP values are highly dependent on several of the parameters analyzed, showing that incorrect data can result from technical and methodological inconsistencies. Considering these differences, we further analyzed the impact of cell variability on GP determination, focusing on basic cell culture conditions, such as cell confluency, number of passages and media composition. Our results show that GP values can report alterations in the biophysical properties of cell membranes caused by cellular adaptation to the culture conditions. In summary, this study provides thorough analysis of the factors that can lead to Laurdan GP variability and suggests approaches to improve data quality, which would generate more precise interpretation and comparison within individual studies and among the literature on Laurdan GP.

Long-term superresolution imaging and quantification of live-cell plasma membrane biophysical properties with smart exchangeable dyes

The study of biological membranes by fluorescence microscopy is hindered by the resolution limit of conventional microscopy. Superresolution microscopy overcomes this problem, but greatly limits temporal resolution. In the case of STED superresolution microscopy, high photobleaching rates prevent long-term imaging. Here, we employ a new exchangeable dye that reports on the molecular order and dynamics of lipid membranes with no photobleaching-induced signal loss. We demonstrate that this dye is sensitive to lipid packing changes in model and cell membranes and perform simultaneous STED-FCS dynamics and packing measurements.

RAS Nanoclusters Selectively Sort Distinct Lipid Headgroups and Acyl Chains.

RAS proteins are lipid-anchored small GTPases that switch between the GTP-bound active and GDP-bound inactive states. RAS isoforms, including HRAS, NRAS and splice variants KRAS4A and KRAS4B, are some of the most frequently mutated proteins in cancer. In particular, constitutively active mutants of KRAS comprise ∼80% of all RAS oncogenic mutations and are found in 98% of pancreatic, 45% of colorectal and 31% of lung tumors. Plasma membrane (PM) is the primary location of RAS signaling in biology and pathology. Thus, a better understanding of how RAS proteins localize to and distribute on the PM is critical to better comprehend RAS biology and to develop new strategies to treat RAS pathology. In this review, we discuss recent findings on how RAS proteins sort lipids as they undergo macromolecular assembly on the PM. We also discuss how RAS/lipid nanoclusters serve as signaling platforms for the efficient recruitment of effectors and signal transduction, and how perturbing the PM biophysical properties affect the spatial distribution of RAS isoforms and their functions.

Nucleated, Outside-Out, Somatic, Macropatch Recordings in Native Neurons.

Patch-clamp recordings are a powerful tool for the live measurement of the plasma membrane biophysical properties, with the ability to discriminate fast events such as fast inactivating Na+ currents (<1ms c.a.). It can be used in virtually every cell-type, including cardiomyocytes, skeletal muscles, neurons, and even epithelial cells and fibroblasts. Voltage-clamp, patch-clamp recordings can be used to measure and characterize the pharmacological and biophysical profile of membrane conductances, including leak, voltage-gated, and ligand-gated ion channels. This technique is particularly useful in studies carried out in cell-lines transfected with the gene expressing the conductance under investigation. However, voltage-clamp measures conducted on the soma of a native, adult neuron, for example in an acute brain slice or in the brain of a live individual, are subject to three major limitations: (1) the branching structure of the neuron causes space-clamp errors, (2) ion channels are differentially expressed across different neuronal compartments (such as soma, dendrites, and axons), and (3) the complex geometry of neurons makes it challenging to calculate current densities. While not preventing the experimenter to conduct patch-clamp, voltage-clamp recordings in native neurons, these limitations make the measures poorly standardized and hence often unusable for testing specific hypotheses.To overcome the limitations outlined above, outside-out, patch-clamp recordings can be carried out instead (See Chap. 1, Sect. 3.5); however, the signal-to-noise ratio in outside-outs from native, adult neurons is usually too low for obtaining accurate measurements.Here we describe how to carry out nucleated, outside-out, somatic, macropatch recordings (from now on abbreviated into "macropatch recordings") to obtain accurate and standardized measures of the biophysical and pharmacological properties of somatic, neuronal membrane conductances.

Ultra-Stable Freestanding Lipid Membrane Array: Direct Visualization of Dynamic Membrane Remodeling with Cholesterol Transport and Enzymatic Reactions.

Cell membranes actively change their local compositions, serving essential biological processes such as cellular signaling and endocytosis. Although membrane dynamics is vital in the cellular functions, the complexity of natural membranes has made its fundamental understanding and systematic assessment difficult. Here, a powerful artificial membrane system is developed for real-time visualization of the spatiotemporal dynamics of membrane remodeling. Through well-defined air/oil/water interfaces on grid holes, tens of planar lipid bilayer membranes are easily created, and their reproducibility, controllability, and generality are highlighted. The freestanding membranes are large but also highly stable, facilitating direct long-term monitoring of dynamic membrane reconstitution caused by external stimuli. As an example to demonstrate the superiority of this membrane system, the effect of cholesterol trafficking, which significantly affects biophysical properties of cell membranes, is investigated at different membrane compositions. Cholesterol transport into and out of the membranes at different rates causes anomalous lipid arrangements through cholesterol-mediated phase transitions and decomposition, which have never been witnessed before. Furthermore, enzyme-induced membrane dynamics is successfully shown in this platform; sphingomyelinases locally generate asymmetry between two membrane leaflets. This technique is broadly applicable for exploring the membrane heterogeneity under various membrane-based reactions, providing valuable insight into the membrane dynamics.

High-Fat Diet-Induced Obesity Modulates Colonic Lgr5 + Stem Cell Homeostasis by Dysregulating Plasma Membrane Organization

Abstract Objectives The emerging obesity epidemic and its co-morbid conditions, such as colorectal cancer, pose a great challenge to global health and healthcare cost. This reinforces the urgent need to elucidate the underlying mechanisms contributing to the promotion of colon cancer in individuals with obesity. Extensive epidemiological studies have demonstrated a consistent and compelling association between obesity and the risk of cancer development and progression. Furthermore, our previous studies demonstrate that obesity induced by high-fat diet results in the expansion of the colonic stem cell pool during cancer initiation. However, the mechanistic link between obesity and the initiation and development of colon cancer remains elusive. Since the biophysical properties of the plasma membrane contribute to cellular signaling, we hypothesized that obesity alters colonic stem cell homeostasis via modulation of the biophysical properties of the plasma membrane, subsequently altering cell signaling events. Methods Our studies utilized complementary in vivo and ex vivo mouse models including colonic organoids. Plasma membrane biophysical properties and cholesterol content were determined utilizing the physico-chemical sensitive dye, Di-4-ANEPPDHQ and Filipin III, respectively. Super-resolution stochastic optical reconstruction microscopy (STORM) was utilized to determine the nanoscale clustering of Wnt receptor, LRP6, and epidermal growth factor receptor (EGFR). Effects of nanoclustering on the activation status of downstream signaling targets was subsequently assessed. Results High-fat diet induced obesity increased plasma membrane free cholesterol and rigidity of colonic crypts and Lgr5+ cells. The increase in rigidity was associated with an increase in the nanoclustering of key stem cell regulating membrane-bound receptors, LRP6 and EGFR. These biophysical perturbations were associated with changes in stem cell signaling and organoid-forming efficiency, a measure of stemness. Conclusions Our results indicate that obesity alters the biophysical properties of the plasma membrane which influences the clustering and downstream signaling of membrane receptors. These findings are noteworthy because they may explain in part how obesity drives colon cancer progression. Funding Sources This work was supported by NIH grant R35CA197707.

Impact of Nanoscale Hindrances on the Relationship between Lipid Packing and Diffusion in Model Membranes.

Membrane models have allowed for precise study of the plasma membrane’s biophysical properties, helping to unravel both structural and dynamic motifs within cell biology. Freestanding and supported bilayer systems are popular models to reconstitute membrane-related processes. Although it is well-known that each have their advantages and limitations, comprehensive comparison of their biophysical properties is still lacking. Here, we compare the diffusion and lipid packing in giant unilamellar vesicles, planar and spherical supported membranes, and cell-derived giant plasma membrane vesicles. We apply florescence correlation spectroscopy (FCS), spectral imaging, and super-resolution stimulated emission depletion FCS to study the diffusivity, lipid packing, and nanoscale architecture of these membrane systems, respectively. Our data show that lipid packing and diffusivity is tightly correlated in freestanding bilayers. However, nanoscale interactions in the supported bilayers cause deviation from this correlation. These data are essential to develop accurate theoretical models of the plasma membrane and will serve as a guideline for suitable model selection in future studies to reconstitute biological processes.

The Quantum-Mechanical Sensitive Na/K Pump Is a Key Mechanism for the Metabolic Control of Neuronal Membrane Function

At present, there are relevant scientific materials on the cellular and molecular mechanisms of electrogenic Na/K pump function and structure, as well as on the potential- and ligand-activated ionic channels in the membrane. However, the role of electrogenic Na/K pump in regulation of semipermeable properties of cell membrane has not been elucidated yet, which is due to the fact that our knowledge about the biophysical properties of cell membrane is based on the conductive membrane theory of Hodgkin-Huxley-Katz, which is developed on internally perfused squid axon and lacks intracellular metabolism. Thus, the accumulated abundance of data on the role of G-proteins-dependent intracellular signaling system in regulation of Na/K pump activity and biophysical properties of cell membrane presumes fundamental revision of some statements of membrane theory. The aim of the present review is to briefly demonstrate our and literature data on cell hydration-induced auto-regulation of Na/K pump as well as on its role in metabolic control of semipermeable properties and excitability of neuronal membrane, which are omitted in the study of internally perfused squid axon.

The effects of dyslipidaemia and cholesterol modulation on erythrocyte susceptibility to malaria parasite infection

BackgroundMalaria disease commences when blood-stage parasites, called merozoites, invade human erythrocytes. Whilst the process of invasion is traditionally seen as being entirely merozoite-driven, emerging data suggests erythrocyte biophysical properties markedly influence invasion. Cholesterol is a major determinant of cell membrane biophysical properties demanding its interrogation as a potential mediator of resistance to merozoite invasion of the erythrocyte.MethodsBiophysical measurements of erythrocyte deformability by flicker spectroscopy were used to assess changes in erythrocyte bending modulus on forced integration of cholesterol and how these artificial changes affect invasion by human Plasmodium falciparum merozoites. To validate these observations in a natural context, either murine Plasmodium berghei or human Plasmodium falciparum merozoites were tested for their ability to invade erythrocytes from a hypercholesterolaemic mouse model or human clinical erythrocyte samples deriving from patients with a range of serum cholesterol concentrations, respectively.ResultsErythrocyte bending modulus (a measure of deformability) was shown to be markedly affected by artificial modulation of cholesterol content and negatively correlated with merozoite invasion efficiency. In an in vitro infection context, however, erythrocytes taken from hypercholesterolaemic mice or from human clinical samples with varying serum cholesterol levels showed little difference in their susceptibility to merozoite invasion. Explaining this, membrane cholesterol levels in both mouse and human hypercholesterolaemia erythrocytes were subsequently found to be no different from matched normal serum controls.ConclusionsBased on these observations, serum cholesterol does not appear to impact on erythrocyte susceptibility to merozoite entry. Indeed, no relationship between serum cholesterol and cholesterol content of the erythrocyte is apparent. This work, nonetheless, suggests that native polymorphisms which do affect membrane lipid composition would be expected to affect parasite entry. This supports investigation of erythrocyte biophysical properties in endemic settings, which may yet identify naturally protective lipid-related polymorphisms.