Dynamics of the suprapatellar bursa during knee joint extension.

PURPOSE: The suprapatellar bursa is located in the proximal deep layer of the patella and is thought to reduce tissue friction by changing from a single-membrane structure to a double-membrane structure during knee joint motion. However, the dynamics of the suprapatellar bursa have only been inferred from positional relationships, and the actual dynamics have not been confirmed. METHODS: Dynamics of the suprapatellar bursa during knee joint motion were observed in eight knees of four Thiel-fixed cadavers and the angle at which the bursa begins to show a double membrane was revealed. The flexion angles of knee joints were measured when the double-membrane structure of the suprapatellar bursa began to appear during knee joint extension. RESULTS: The suprapatellar bursa changes from a single membrane to a double-membrane structure at 91 ± 4° of flexion, when the knee joint is moved from a flexed position to an extended position. CONCLUSION: The suprapatellar bursa may be involved in limitations to knee joint range of motion and pain at an angle of approximately 90°. Further studies are needed to verify whether the same dynamics are observed in living subjects.

Partitioning to ordered membrane domains regulates the kinetics of secretory traffic.

The organelles of eukaryotic cells maintain distinct protein and lipid compositions required for their specific functions. The mechanisms by which many of these components are sorted to their specific locations remain unknown. While some motifs mediating subcellular protein localization have been identified, many membrane proteins and most membrane lipids lack known sorting determinants. A putative mechanism for sorting of membrane components is based on membrane domains known as lipid rafts, which are laterally segregated nanoscopic assemblies of specific lipids and proteins. To assess the role of such domains in the secretory pathway, we applied a robust tool for synchronized secretory protein traffic (RUSH, Retention Using Selective Hooks) to protein constructs with defined affinity for raft phases. These constructs consist solely of single-pass transmembrane domains (TMDs) and, lacking other sorting determinants, constitute probes for membrane domain-mediated trafficking. We find that while raft affinity can be sufficient for steady-state PM localization, it is not sufficient for rapid exit from the endoplasmic reticulum (ER), which is instead mediated by a short cytosolic peptide motif. In contrast, we find that Golgi exit kinetics are highly dependent on raft affinity, with raft preferring probes exiting the Golgi ~2.5-fold faster than probes with minimal raft affinity. We rationalize these observations with a kinetic model of secretory trafficking, wherein Golgi export can be facilitated by protein association with raft domains. These observations support a role for raft-like membrane domains in the secretory pathway and establish an experimental paradigm for dissecting its underlying machinery.

New insights into the destabilization of fat globules in ultra-instantaneous UHT milk induced by added plasmin: Molecular mechanisms and the effect of membrane structure on plasmin action.

Residual plasmin activity in whole ultra-instantaneous UHT (UI-UHT) milk causes rapid fat rise during storage, seriously affecting consumers' purchase intentions. In this work, the molecular mechanisms underlying fat destabilization in whole UI-UHT milk by added plasmin were investigated based on the hydrolysis behavior of interfacial proteins. By using SDS-PAGE and peptidomic analysis, we found that the hydrolysis of interfacial proteins by plasmin led to a decrease in the amount and coverage of interfacial proteins and an increase in zeta-potential value, causing the flocculation and coalescence of fat globules. Moreover, the hydrolysis pattern varied in different categories of interfacial proteins by plasmin. In total, 125 peptides in all samples were identified. Plasmin tended to hydrolyze most major milk fat globule membrane (MFGM) proteins into protein fragments (>10 kDa) rather than peptides (<10 kDa). In contrast, peptides derived from caseins were more preferentially identified within a relatively short incubation time. It was the co-hydrolysis of caseins and some major MFGM proteins as anchors that destroyed the stability of MFGM. Furthermore, studies on the effect of trilayer membrane structure remaining at the interface on the hydrolysis rate of major MFGM proteins by plasmin revealed that ADPH and BTN were very sensitive to plasmin action, while PAS 7 was very resistant to plasmin action. Overall, membrane structure reduced the susceptibility of some major MFGM proteins to plasmin and provided protective effects. Therefore, this study provided important insights into the hydrolysis behavior of interfacial proteins in whole UI-UHT milk induced by plasmin.

Effect of cholesterol-loaded cyclodextrin treatment on boar sperm cryopreservation.

Objective: This study investigated the efficacy of different concentrations of Cholesterol-loaded cyclodextrin (CLC) on cryopreservation in boar sperm quality. Methods: In this study, we treated boar sperm with different concentrations of CLC before freezing and analyzed the sperm cholesterol concentration, plasma membrane, acrosome integrity rate and total motility rate before and after freeze-thawing. We also investigated the levels of reactive oxygen species (ROS), malondialdehyde (MDA), ATP, and structural- and oxidative-damage related proteins in all groups after thawing. Results: The results revealed that the cholesterol concentration of the CLC-treated groups was higher than that of the control group, both before freezing and after thawing (p < 0.05). The plasma membrane integrity rate, acrosome integrity rate, and total motility rate of sperm were also enhanced after thawing in the CLC-treated group (all p < 0.05). Moreover, ROS and MDA production and ATP loss were reduced in CLC-treated sperm during freezing and thawing (p < 0.05). Finally, CLC pretreatment partially prevented the consumption of various proteins involved in metabolism including CAPZB, HSP90AA1 and PGAM2 (p < 0.05). Conclusion: CLC treatment increased cholesterol concentration and decreased structural injury and oxidative damage during boar sperm freezing and thawing, improving the efficacy of sperm cryopreservation in boar.

Notable enhancement of Amphotericin B channel activity by applied pressures in the range of MS channel activation.

The mechanism of Amphotericin B at the membrane is still subject of debate, with the prevailing hypothesis being the formation of pores. The activity of these pores is influenced by various factors. Recently aggregation in solution and insertion in the membrane had been highlighted as crucial for action of the drug Here we investigated the effect of applied pressure on the activity of Amphotericin B. Our findings demonstrate that applied pressure of 50 mmHg is sufficient to enhance the activity. We interpreted the results as supporting the idea that pressure fractures the membrane and promotes the insertion of the polyene.

Effect of citric acid on cell membrane structure and function of Issatchenkia terricola WJL-G4.

AIMS: This study aimed to investigate the changes of cell membrane structure and function of Issatchenkia terricola under citric acid by performing physiological analysis. METHODS AND RESULTS: The membrane integrity, surface hydrophobicity, structure, fluidity, apoptosis, and fatty acid methyl esters composition of I. terricola WJL-G4 cells were determined by propidium iodide staining, microbial adhesion to hydrocarbon test, transmission electron microscopy analysis, fluorescence anisotropy, flow cytometry, and gas chromatography-mass, respectively. The results showed that with the increasing of citric acid concentrations, the cell vitality, membrane integrity, and fluidity of I. terricola reduced; meanwhile, apoptosis rate, membrane permeable, hydrophobicity, and ergosterol contents augmented significantly. Compared to control, the activities of Na+, K+-ATPase, and Ca2+, Mg2+-ATPase increased by 3.73-fold and 6.70-fold, respectively, when citric acid concentration increased to 20 g l-1. The cells cracked and their cytoplasm effused when the citric acid concentration reached 80 g l-1. CONCLUSIONS: I. terricola could successfully adjust its membrane structure and function below 60 g l-1 of citric acid. However, for citric acid concentrations above 80 g l-1, its structure and function were dramatically changed, which might result in reduced functionality.

Utilization of low-temperature heating method to improve skim milk production: Microstructure, stability, and constituents of milk fat globule membrane.

In the process of defatting milk, preheating treatment is an important factor affecting the flavor of skim milk. Here, raw milk was preheated at different times and temperatures. Then laser confocal microscopy, multiple-light scattering instrument, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) were used to analyze the microstructure of milk fat globule membrane (MFGM), milk stability, and MFGM protein (MFGMP) components. Results showed that phospholipid domain of MFGM changed from an ordered state (Lo) to a disordered state (Ld) with increase in treatment temperature and time, leading to an increase in MFGMP content in skim milk. During the stability test, the stability of raw milk decreased significantly with increase in preheating temperature, while the opposite was true for skim milk. Finally, the results of MFGMP differentiation analysis showed that, the content of ten taste-related MFGMPs in the control group samples was significantly lower compared to the optimal group (P < 0.05).

Identification of the toxin components of Rhizoctonia solani AG1-IA and its destructive effect on plant cell membrane structure.

Rice sheath blight is a fungal disease caused mainly by Rhizoctonia solani AG1-IA. Toxins are a major pathogenic factor of R. solani, and some studies have reported their toxin components; however, there is no unified conclusion. In this study, we reported the toxin components and their targets that play a role in R. solani AG1-IA. First, toxins produced by R. solani AG1-IA were examined. Several important phytotoxins, including benzoic acid (BZA), 5-hydroxymethyl-2-furanic aid (HFA), and catechol (CAT), were identified by comparative analysis of secondary metabolites from AG1-IA, AG1-IB, and healthy rice. Follow-up studies have shown that the toxin components of this fungus can rapidly disintegrate the biofilm structure while maintaining the content of host plant membrane components, thereby affecting the organelles, which may also explain the lack of varieties highly resistant to sheath blight.

The small-molecule kinase inhibitor ceritinib, unlike imatinib, causes a significant disturbance of lipid membrane integrity: A combined experimental and MD study.

Ceritinib and imatinib are small-molecule protein kinase inhibitors which are applied as therapeutic agents against various diseases. The fundamentals of their clinical use, i.e. their pharmacokinetics as well as the mechanisms of the inhibition of the respective kinases, are relatively well studied. However, the interaction of the drugs with membranes, which can be a possible cause of side effects, has hardly been investigated so far. Therefore, we have characterized the interaction of both drugs with lipid membranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the absence and in the presence of cholesterol. For determining the membrane impact of both drugs on a molecular level, different experimental (NMR, ESR, fluorescence) and theoretical (MD simulations) approaches were applied. The data show that ceritinib, in contrast to imatinib, interacts more effectively with membranes significantly affecting various physico-chemical membrane parameters like membrane order and transmembrane permeation of polar solutes. The pronounced membrane impact of ceritinib can be explained by a strong affinity of the drug towards POPC which competes with the POPC-cholesterol interaction by that attenuating the ordering effect of cholesterol. The data are relevant for understanding putative toxic and cytotoxic side effects of these drugs such as the triggering of cell lysis or apoptosis.

Effects of ionic liquids on biomembranes: A review on recent biophysical studies.

Ionic liquids (ILs) have been emerged as a versatile class of compounds that can be easily tuned to achieve desirable properties for various applications. The ability of ILs to interact with biomembranes has attracted significant interest, as they have been shown to modulate membrane properties in ways that may have implications for various biological processes. This review provides an overview of recent studies that have investigated the interaction between ILs and biomembranes. We discuss the effects of ILs on the physical and chemical properties of biomembranes, including changes in membrane fluidity, permeability, and stability. We also explore the mechanisms underlying the interaction of ILs with biomembranes, such as electrostatic interactions, hydrogen bonding, and van der Waals forces. Additionally, we discuss the future prospects of this field.

DODAB vesicles containing lysophosphatidylcholines: The relevance of acyl chain saturation on the membrane structure and thermal properties.

The saturated LPC18:0 and unsaturated LPC18:1 lysophosphatidylcholines have important roles in inflammation and immunity and are interesting targets for immunotherapy. The synthetic cationic lipid DODAB has been successfully employed in delivery systems, and would be a suitable carrier for those lysophosphatidylcholines. Here, assemblies of DODAB and LPC18:0 or LPC18:1 were characterized by Differential Scanning Calorimetry (DSC) and Electron Paramagnetic Resonance (EPR) spectroscopy. LPC18:0 increased the DODAB gel-fluid transition enthalpy and rigidified both phases. In contrast, LPC18:1 caused a decrease in the DODAB gel-fluid transition temperature and cooperativity, associated with two populations with distinct rigidities in the gel phase. In the fluid phase, LPC18:1 increased the surface order but, differently from LPC18:0, did not affect viscosity at the membrane core. The impact of the different acyl chains of LPC18:0 and 18:1 on structure and thermotropic behavior should be considered when developing applications using mixed DODAB membranes.

Self-Standing, Ultrasonic Spray-Deposited Membranes for Fuel Cells.

The polymer electrolyte membrane and its contact with electrodes has a significant effect on the performance of fuel and electrolysis cells but the choice of commercially available membranes is limited. In this study, membranes for direct methanol fuel cells (DMFCs) were made by ultrasonic spray deposition from commercial Nafion solution; the effect of the drying temperature and presence of high boiling solvents on the membrane properties was then analyzed. When choosing suitable conditions, membranes with similar conductivity, water uptake, and higher crystallinity than comparable commercial membranes can be obtained. These show similar or superior performance in DMFC operation compared to commercial Nafion 115. Furthermore, they exhibit low permeability for hydrogen, which makes them attractive for electrolysis or hydrogen fuel cells. The findings from our work will allow for the adjustment of membrane properties to the specific requirements of fuel cells or water electrolysis, as well as the inclusion of additional functional components for composite membranes.

Simple Method for the Creation of a Bacteria-Sized Unilamellar Liposome with Different Proteins Localized to the Respective Sides of the Membrane.

Artificial cells are membrane vesicles mimicking cellular functions. To date, giant unilamellar vesicles made from a single lipid membrane with a diameter of 10 µm or more have been used to create artificial cells. However, the creation of artificial cells that mimic the membrane structure and size of bacteria has been limited due to technical restrictions of conventional liposome preparation methods. Here, we created bacteria-sized large unilamellar vesicles (LUVs) with proteins localized asymmetrically to the lipid bilayer. Liposomes containing benzylguanine-modified phospholipids were prepared by combining the conventional water-in-oil emulsion method and the extruder method, and green fluorescent protein fused with SNAP-tag was localized to the inner leaflet of the lipid bilayer. Biotinylated lipid molecules were then inserted externally, and the outer leaflet was modified with streptavidin. The resulting liposomes had a size distribution in the range of 500-2000 nm with a peak at 841 nm (the coefficient of variation was 10.3%), which was similar to that of spherical bacterial cells. Fluorescence microscopy, quantitative evaluation using flow cytometry, and western blotting proved the intended localization of different proteins on the lipid membrane. Cryogenic electron microscopy and quantitative evaluation by α-hemolysin insertion revealed that most of the created liposomes were unilamellar. Our simple method for the preparation of bacteria-sized LUVs with asymmetrically localized proteins will contribute to the creation of artificial bacterial cells for investigating functions and the significance of their surface structure and size.

Lipid domain boundary triggers membrane damage and protein folding of human islet amyloid polypeptide in the early pathogenesis of amyloid diseases.

The misfolding and self-aggregation of human Islet Amyloid Polypeptide (hIAPP) are linked to the onset of type 2 diabetes (T2D). However, the mechanism of how the disordered hIAPP aggregates trigger membrane damage leading to the loss of Islet cells in T2D is unknown. Using coarse-grained (CG) and all-atom (AA) molecular dynamics simulations, we have investigated the membrane-disruption behaviors of hIAPP oligomers on the phase-separated lipid nanodomains that mimic the highly heterogeneous lipid raft structures of cell membranes. Our results revealed that hIAPP oligomers preferentially bind to the liquid-ordered and liquid-disordered domain boundary around two hydrophobic residues at L16 and I26, and lipid acyl chain order disruption and beta-sheet formation occur upon hIAPP binding to the membrane surface. We propose that the lipid order disruption and surface-induced beta-sheet formation on the lipid domain boundary represent the early molecular events of membrane damage associated with the early pathogenesis of T2D.

In vitro anti-Toxoplasma gondii effects of a coccidiostat dinitolmide.

Coccidiosis, caused by Eimeria species, results in huge economic losses to the animal industry. Dinitolmide, a veterinary-approved coccidiostat, has a wide anticoccidial spectrum with no effect on host immunity. However, the mechanism of its anticoccidial effects remains unclear. Here, we used an in vitro culture system of T. gondii to explore the anti-Toxoplasma effect of dinitolmide and its underlying mechanism against coccidia. We show that dinitolmide has potent in vitro anti-Toxoplasma activity with the half-maximal effective concentration (EC50) of 3.625 µg/ml. Dinitolmide treatment significantly inhibited the viability, invasion and proliferation of T. gondii tachyzoites. The recovery experiment showed that dinitolmide can completely kill T. gondii tachyzoites after 24 h of treatment. Morphologically abnormal parasites were observed after dinitolmide exposure, including asynchronous development of daughter cells and deficiency of parasite inner and outer membrane. Further electron microscopy results showed that the drug could damage the membrane structure of T. gondii. By comparative transcriptomic analysis, we found that genes related to cell apoptosis and nitric-oxide synthase were up-regulated after dinitolmide treatment, which might be responsible for parasite cell death. Meanwhile, many Sag-related sequence (srs) genes were down-regulated after treatment, which could be closely associated with the reduction of parasite invasion and proliferation capacity. Our study indicates that the coccidiostat dinitolmide has a potent inhibitory effect on T. gondii in vitro and provides insight into the mode of action of the drug.

Precise Construction of Sn/C Composite Membrane with Graphene-Like Sn-in-Carbon Structural Units toward Hyperstable Anode for Lithium Storage.

A new-type binder-free Sn/C composite membrane with densely stacked Sn-in-carbon nanosheets was prepared by vacuum-induced self-assembly of graphene-like Sn alkoxide and following in situ thermal conversion. The successful implementation of this rational strategy is based on the controllable synthesis of graphene-like Sn alkoxide by using Na-citrate with the critical inhibitory effect on polycondensation of Sn alkoxide along the a and b directions. Density functional theory calculations reveal that graphene-like Sn alkoxide can be formed under the joint action of oriented densification along the c axis and continuous growth along the a and b directions. The Sn/C composite membrane constructed by graphene-like Sn-in-carbon nanosheets can effectively buffer volume fluctuation of inlaid Sn during cycling and much enhance the kinetics of Li+ diffusion and charge transfer with the developed ion/electron transmission paths. After temperature-controlled structure optimization, Sn/C composite membrane displays extraordinary Li storage behaviors, including reversible half-cell capacities up to 972.5 mAh g-1 at a density of 1 A g-1 for 200 cycles, 885.5/729.3 mAh g-1 over 1000 cycles at large current densities of 2/4 A g-1, and terrific practicability with reliable full-cell capacities of 789.9/582.9 mAh g-1 up to 200 cycles under 1/4 A g-1. It is worthy of noting that this strategy may open up new opportunities to fabricate advanced membrane materials and construct hyperstable self-supporting anodes in lithium ion batteries.

Inactivation effects and mechanism of ohmic heating on Bacillus cereus.

The inactivation effects and mechanism of ohmic heating (OH) on Bacillus cereus ATCC 11778 were investigated in this study, conventional heating (CH) was also carried out and served as control. All OH treatments (10 V/cm 50 Hz, 10 V/cm 500 Hz, 5 V/cm 50 Hz and 5 V/cm 500 Hz) could achieve a comparable inactivation effect with CH, while OH treatments significantly shortened the processing time. OH treated cells exhibited significantly higher leakage of metal ions (Mg2+ and K+) and biomacromolecules (nucleic acids and proteins) than those treated with CH when bacterial suspensions were heated to the same temperature. Moreover, OH treatment caused more damage on membrane structure, greatly decreased the cell membrane potential and endogenous enzyme activity than that of CH. The results of this study indicated that OH is more efficient in the inactivation of bacteria.

Fifty Years of Biophysics at the Membrane Frontier.

The author first describes his childhood in the South and the ways in which it fostered the values he has espoused throughout his life, his development of a keen fascination with science, and the influences that supported his progress toward higher education. His experiences in ROTC as a student, followed by two years in the US Army during the Vietnam War, honed his leadership skills. The bulk of the autobiography is a chronological journey through his scientific career, beginning with arrival at the University of California, Irvine in 1972, with an emphasis on the postdoctoral students and colleagues who have contributed substantially to each phase of his lab's progress. White's fundamental findings played a key role in the development of membrane biophysics, helping establish it as fertile ground for research. A story gradually unfolds that reveals the deeply collaborative and painstakingly executed work necessary for a successful career in science.

The Fluid-Mosaic model of cell membranes: A brief introduction, historical features, some general principles, and its adaptation to current information.

The Fluid-Mosaic Membrane (FMM) model was originally proposed as a general, nanometer-scale representation of cell membranes (Singer and Nicolson, 1972). The FMM model was based on some general principles, such as thermodynamic considerations, intercalation of globular proteins into a lipid bilayer, independent protein and lipid dynamics, cooperativity and other characteristics. Other models had trimolecular structures or membrane globular lipoprotein units. These latter models were flawed, because they did not allow autonomous lipids, membrane domains or discrete lateral dynamics. The FMM model was also consistent with membrane asymmetry, cis- and trans-membrane linkages and associations of membrane components into multi-molecular complexes and domains. It has remained useful for explaining the basic organizational principles and properties of various biological membranes. New information has been added, such as membrane-associated cytoskeletal assemblies, extracellular matrix interactions, transmembrane controls, specialized lipid-protein domains that differ in compositions, rotational and lateral mobilities, lifetimes, functions, and other characteristics. The presence of dense, structured membrane domains has reduced significantly the extent of fluid-lipid membrane areas, and the FMM model is now considered to be more mosaic and dense than the original proposal.

Membrane skeleton hyperstability due to a novel alternatively spliced 4.1R can account for ellipsoidal camelid red cells with decreased deformability.

The red blood cells (RBCs) of vertebrates have evolved into two basic shapes, with nucleated nonmammalian RBCs having a biconvex ellipsoidal shape and anuclear mammalian RBCs having a biconcave disk shape. In contrast, camelid RBCs are flat ellipsoids with reduced membrane deformability, suggesting altered membrane skeletal organization. However, the mechanisms responsible for their elliptocytic shape and reduced deformability have not been determined. We here showed that in alpaca RBCs, protein 4.1R, a major component of the membrane skeleton, contains an alternatively spliced exon 14-derived cassette (e14) not observed in the highly conserved 80 kDa 4.1R of other highly deformable biconcave mammalian RBCs. The inclusion of this exon, along with the preceding unordered proline- and glutamic acid-rich peptide (PE), results in a larger and unique 90 kDa camelid 4.1R. Human 4.1R containing e14 and PE, but not PE alone, showed markedly increased ability to form a spectrin-actin-4.1R ternary complex in viscosity assays. A similar facilitated ternary complex was formed by human 4.1R possessing a duplication of the spectrin-actin-binding domain, one of the mutations known to cause human hereditary elliptocytosis. The e14- and PE-containing mutant also exhibited an increased binding affinity to ß-spectrin compared with WT 4.1R. Taken together, these findings indicate that 4.1R protein with the e14 cassette results in the formation and maintenance of a hyperstable membrane skeleton, resulting in rigid red ellipsoidal cells in camelid species, and suggest that membrane structure is evolutionarily regulated by alternative splicing of exons in the 4.1R gene.