61 research outputs found
Leakage and lysis of lipid membranes induced by the lipopeptide surfactin
Surfactin is a lipopeptide produced by Bacillus subtilis which possesses antimicrobial activity. We have studied the leakage and lysis of POPC vesicles induced by surfactin using calcein fluorescence de-quenching, isothermal titration calorimetry and 31P solid state NMR. Membrane leakage starts at a surfactin-to-lipid ratio in the membrane, R b≈0.05, and an aqueous surfactin concentration of C S w ≈2μM. The transient, graded nature of leakage and the apparent coupling with surfactin translocation to the inner leaflet of the vesicles, suggests that this low-concentration effect is due to a bilayer-couple mechanism. Different permeabilization behaviour is found at R b≈0.15 and attributed to surfactin-rich clusters, which can induce leaks and stabilize them by covering their hydrophobic edges. Membrane lysis or solubilization to micellar structures starts at R b sat =0.22 and C S w =9μM and is completed at R m sol =0.43 and C S w =11μM. The membrane-water partition coefficient of surfactin is obtained as K=2×104M−1. These data resolve inconsistencies in the literature and shed light on the variety of effects often referred to as detergent-like effects of antibiotic peptides on membranes. The results are compared with published parameters characterizing the hemolytic and antibacterial activit
Gradual Change or Phase Transition: Characterizing Fluid Lipid-Cholesterol Membranes on the Basis of Thermal Volume Changes
AbstractCholesterol has been reported to govern biomembrane permeability, elasticity, and the formation of lipid rafts. There has been a controversy whether binary lipid-cholesterol membranes should better be described in terms of a phase separation (liquid-ordered and liquid-disordered phases) or of gradual changes in largely homogeneous membranes. We present a new approach for detecting and characterizing phase equilibria in colloidal dispersions using pressure perturbation calorimetry (PPC). We apply this to the study of the thermal expansivity of mixtures of 1-palmitoyl-2-oleoyl sn-glycero-3-phosphatidylcholine (POPC) and cholesterol as a function of composition and temperature. We show that cholesterol can condense lipids not only laterally (with respect to interfacial area) but also in volume. A quantitative comparison with expansivity curves simulated assuming either phase separation or random mixing within one phase reveals that the real system shows an intermediate behavior due to submicroscopic demixing effects. However, both models yield consistent system parameters and are thus found to be useful for describing the systems to a similar approximation. Accordingly, one cholesterol may condense 3±1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine molecules by ∼−(1.4±0.5) vol % at 2°C; both absolute values decrease with increasing temperature
Superior Membrane Permeabilization and Solubilization Properties of Biosurfactants may be Explained by Heterogeneous Perturbation
Folding Thermodynamics of the Hybrid-1 Type Intramolecular Human Telomeric GQuadruplex
Guanine-rich DNA sequences that may form
G-quadruplexes are located in strategic DNA loci with
the ability to regulate biological events. G-quadruplexes
have been under intensive scrutiny owing to their potential
to serve as novel drug targets in emerging anticancer
strategies. Thermodynamic characterization of
G-quadruplexes is an important and necessary step in
developing predictive algorithms for evaluating the conformational
preferences of G-rich sequences in the presence
or the absence of their complementary C-rich
strands. We use a combination of spectroscopic, calorimetric,
and volumetric techniques to characterize the
folding/unfolding transitions of the 26-meric human telomeric
sequence d[A3G3(T2AG3)3A2]. In the presence of
K1 ions, the latter adopts the hybrid-1 G-quadruplex
conformation, a tightly packed structure with an unusually
small number of solvent-exposed atomic groups. The
K1-induced folding of the G-quadruplex at room temperature
is a slow process that involves significant accumulation
of an intermediate at the early stages of the
transition. The G-quadruplex state of the oligomeric
sequence is characterized by a larger volume and compressibility
and a smaller expansibility than the coil state.
These results are in qualitative agreement with each other
all suggesting significant dehydration to accompany the
G-quadruplex formation. Based on our volume data,
432619 water molecules become released to the bulk
upon the G-quadruplex formation. This large number is
consistent with a picture in which DNA dehydration is
not limited to water molecules in direct contact with the
regions that become buried but involves a general
decrease in solute–solvent interactions all over the surface
of the folded structure. VC 2013 Wiley Periodicals, Inc.
Biopolymers 101: 216–227, 2014.
Keywords: G-quadruplexes; conformational transitions;
volume; compressibility; expansibilit
Finding the Right Straw in a Haystack: How Lipid-Detergent Interactions may Affect the Solubilisation and Reconstitution of Membrane Proteins
Application of pressure perturbation calorimetry to lipid bilayers.
Pressure perturbation calorimetry (PPC) is a new method that measures the heat consumed or released by a sample after a sudden pressure jump. The heat change can be used to derive the thermal volume expansion coefficient, alpha(V), as a function of temperature and, in the case of phase transitions, the volume change, DeltaV, occurring at the phase transition. Here we present the first report on the application of PPC to determine these quantities for lipid bilayers. We measure the volume changes of the pretransition and main transition of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and the thermal expansivity of the fluid phase of DMPC and of two unsaturated lipids, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. The high sensitivity of PPC instrumentation gives accurate data for alpha(V) and DeltaV even upon the application of relatively low pressures of approximately 5 bar
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