Biochimica et biophysica acta. Biomembranes最新文献

Arginine-based surfactants exhibit antimicrobial activity attributed to their positive net charge and amphiphilic nature. These compounds typically disrupt cytoplasmic membranes, leading to cell leakage. We studied the mechanism of action of N^α-benzoyl-L-arginine dodecylamide (Bz-Arg-NHC₁₂), an arginine-based surfactant synthesized in our laboratory through biocatalysis, using model lipid membranes. Bz-Arg-NHC₁₂ shows selective membrane interactions, which correlate with its antimicrobial efficacy and haemolytic toxicity. In bacterial-like membranes, it penetrates deeply, increasing elasticity and destabilizing the membrane, leading to rapid vesicle permeabilization via sudden and graded lysis. Monolayer studies confirm strong electrostatic perturbations, consistent with dipole enhancement. For mammalian-like membranes, Bz-Arg-NHC₁₂ incorporation appears as more superficial, preferentially partitioning into cholesterol-rich liquid-ordered domains in giant unilamellar vesicles. Surfactant enrichment stabilizes membranes and induces slow vesicle permeabilization, with lysis occurring primarily through graded mechanisms. Sub-lytic concentrations induce vesicle aggregation, while membrane solubilization aligns with higher thresholds. These findings highlight the potential surfactant's therapeutic window: deep bacterial membrane disruption drives antimicrobial action, while cholesterol-mediated superficial incorporation in mammalian membranes delays toxicity. Phase-selective liquid-ordered-domain localization may further enhance selectivity. These results provide a biophysical-based rationale for optimizing arginine surfactants as next-generation biocides.

An important class of lipids found in biological membranes is composed of two structurally different hydrocarbon chains. Among these, low-melting lipids possessing both a saturated and unsaturated chain have been intensely studied because of their biological abundance and influence on lipid rafts. In contrast, much less is known about the biophysical effects of mixed chains in high-melting lipids. Here, we investigated two such lipids-MSPC (14:0-18:0 PC) and SMPC (18:0-14:0 PC)-to determine how chain length mismatch and acyl chain position on the glycerol backbone influence lateral organization. We studied the temperature- and composition-dependent phase behavior of liposomes composed of either mixed-chain or symmetric-chain high-melting lipids plus DOPC and cholesterol, using techniques sensitive to domain formation at both microscopic and nanoscopic length scales. All studied mixtures exhibited liquid-ordered (Lo) + liquid-disordered (Ld) phase coexistence with domains that were visible in confocal microscopy experiments. FRET measurements showed that all mixtures also exhibited nanoscopic heterogeneity at temperatures above the microscopic miscibility transition temperature, and cryo-EM imaging further revealed bilayer thickness variation consistent with coexisting Ld and Lo phases. Both the microscopic miscibility transition temperature, μm-T_mix, and its nanoscopic counterpart, nm-T_mix, were strongly correlated with the melting transition temperature of the saturated lipid; the sole exception was SMPC/DOPC/Chol, whose μm-T_mix showed a significant negative deviation from the expected value, implying an enhanced propensity for nanoscopic phase separation in mixtures containing this high-melting species. These results point to strong effects of acyl chain position within mixed-chain high-T_M lipids on the microscopic phase behavior of ternary mixtures.

The binding of local anesthetics (LAs) to cell membranes is required for LAs to reach the target ion channels, but lipid interactions may also play a role in a purely membrane-mediated mode of activity. Here, we used solid-state NMR and further biophysical techniques to characterize the effect of six LAs covering a wide range of structures and properties (benzocaine, bupivacaine, mepivacaine, lidocaine, procaine, QX-314) on membranes. Membrane partitioning log D values (between 2.1 and 3.7) varied little with pH, in contrast to octanol partitioning. Membrane thinning was induced by most LAs, except for benzocaine. A conformational change in the lipid headgroup was observed, with a pronounced dependence on the protonation state, indicating the importance of the positive charge that is maintained by most membrane-bound LAs. We found stabilization of negative membrane curvature in the case of benzocaine, and of positive curvature in the case of bupivacaine, procaine, mepivacaine and, most pronouncedly, for QX-314. Comparing the LAs with respect of their influence on membranes as observed in the different experiments, benzocaine and QX-314 were always found at either extreme of the scale, with bupivacaine and lidocaine closer in their effect to benzocaine. This order of influence correlates with the depth of membrane insertion and with the protonation state, both of which were identified as key factors for LA behavior. Finally, we found indications that LAs are able to alter the activity of bacterial mechanosensitive channels without any expected LA binding sites, thus supporting a membrane-mediated activity of LAs.

We present a robust and easy-to-use methodology for determining the nanoscopic miscibility transition temperature, nm-T_mix, of lipid bilayer mixtures from FRET measurements. The method relies on the use of freely diffusing fluorescent donor and acceptor lipids that partition non-uniformly between coexisting phases. When this condition is met, changes in lipid clustering that occur as the sample passes through the transition result in abrupt changes in the spatial distribution of probes and consequently, abrupt changes in the FRET signal. FRET vs. temperature data can then be modeled with a phenomenological piecewise function that describes how the signal changes above and below nm-T_mix. Using lattice simulations, we show that the transition between these regimes occurs when the size of lipid clusters surpasses a critical threshold that is approximately equal to twice the Förster distance of the donor/acceptor pair, or about 10 nm. Because other, temperature-dependent factors unrelated to lateral organization-such as changes in lipid molecular area and donor photophysics-can also influence the FRET signal, we also fit the data using a simpler model of uniform mixing. An information theory-based test comparing the fit quality of the uniform and phase separated models provides a straightforward and robust criterion for objectively assessing whether a given sample undergoes a nanoscopic miscibility transition within a temperature range of interest. We highlight the distinction between nm-T_mix determined by FRET (or methods with comparable spatial resolution) and the micron-scale transition temperature, μm-T_mix, determined from diffraction-limited optical techniques. The analysis software is freely available from an online repository.

Plants produce natural rubber in specialized organelles, termed rubber particles (RP). The structure of the RP consists of a polyisoprene (rubber) core surrounded by a shell layer composed of a lipid monolayer and proteins. Among the prominent RP-associated proteins is small rubber particle protein (SRPP), the second most abundant protein on the Hevea brasiliensis rubber particle monolayer membrane. In this study, a combination of protein modeling, biophysical analysis, biochemistry, and transmission electron microscopy have been utilized to further characterize Hevea SRPP1 (HbSRPP1) membrane architectural rearrangement capabilities. Results obtained reveal that HbSRPP1 possesses characteristics reminiscent of apolipoproteins, including the ability to reorganize aqueous phospholipid dispersions into stable, disk-shaped nanoparticles, termed nanodisks. This research provides the groundwork for further studies into the mechanism of SRPP's interaction with the RP membrane surface which likely involves conformational changes in RP topology.