Interaction of antimicrobial peptide Plantaricin149a and four analogs with lipid bilayers and bacterial membranes

The amidated analog of Plantaricin149, an antimicrobial peptide from Lactobacillus plantarum NRIC 149, directly interacts with negatively charged liposomes and bacterial membranes, leading to their lysis. In this study, four Pln149-analogs were synthesized with different hydrophobic groups at their N-terminus with the goal of evaluating the effect of the modifications at this region in the peptide's antimicrobial properties. The interaction of these peptides with membrane models, surface activity, their hemolytic effect on red blood cells, and antibacterial activity against microorganisms were evaluated. The analogs presented similar action of Plantaricin149a; three of them with no hemolytic effect (< 5%) until 0.5 mM, in addition to the induction of a helical element when binding to negative liposomes. The N-terminus difference between the analogs and Plantaricin149a retained the antibacterial effect on S. aureus and P. aeruginosa for all peptides (MIC50 of 19 µM and 155 µM to Plantaricin149a, respectively) but resulted in a different mechanism of action against the microorganisms, that was bactericidal for Plantaricin149a and bacteriostatic for the analogs. This difference was confirmed by a reduction in leakage action for the analogs. The lytic activity of Plantaricin149a is suggested to be a result of the peptide-lipid interactions from the amphipathic helix and the hydrophobic residues at the N-terminus of the antimicrobial peptide.

MAPS: An interactive web server for membrane annotation of transmembrane protein structures.

The exact positioning of the membrane in transmembrane (TM) proteins plays important functional roles. Yet, the structures of TM proteins in protein data bank (pdb) have no information about the explicit position of the membrane. Using a simple hydrophobic lipid-protein mismatch energy function and a flexible lipid/water boundary, the position of lipid bilayer for representative TM proteins in pdb have been annotated. A web server called MAPS (Membrane Annotation of Protein Structures; available at: http://www.boseinst.ernet.in/gautam/maps) has been set up that allows the user to interactively analyze membrane-protein orientations of any uploaded pdb structure with user-defined membrane flexibility parameters.

The effect of hydrostatic pressure on membrane-bound proteins

Many cellular proteins are bound to the surfaces of membranes and participate in various cell signaling responses. Interactions between this group of proteins are in part controlled by the membrane surface to which the proteins are bound. This review focuses on the effects of pressure on membrane-associated proteins. Initially, the effect of pressure on membrane surfaces and how pressure may perturb the membrane binding of proteins is discussed. Next, the effect of pressure on the activity and lateral association of proteins is considered. We then discuss how pressure can be used to gain insight into these types of proteins.

Cholesterol-dependent hemolytic activity of Passiflora quadrangularis leaves

Plants used in traditional medicine are rich sources of hemolysins and cytolysins, which are potential bactericidal and anticancer drugs. The present study demonstrates for the first time the presence of a hemolysin in the leaves of Passiflora quadrangularis L. This hemolysin is heat stable, resistant to trypsin treatment, has the capacity to froth, and acts very rapidly. The hemolysin activity is dose-dependent, with a slope greater than 1 in a double-logarithmic plot. Polyethylene glycols of high molecular weight were able to reduce the rate of hemolysis, while liposomes containing cholesterol completely inhibited it. In contrast, liposomes containing phosphatidylcholine were ineffective. The Passiflora hemolysin markedly increased the conductance of planar lipid bilayers containing cholesterol but was ineffective in cholesterol-free bilayers. Successive extraction of the crude hemolysin with n-hexane, chloroform, ethyl acetate, and n-butanol resulted in a 10-fold purification, with the hemolytic activity being recovered in the n-butanol fraction. The data suggest that membrane cholesterol is the primary target for this hemolysin and that several hemolysin molecules form a large transmembrane water pore. The properties of the Passiflora hemolysin, such as its frothing ability, positive color reaction with vanillin, selective extraction with n-butanol, HPLC profile, cholesterol-dependent membrane susceptibility, formation of a stable complex with cholesterol, and rapid erythrocyte lysis kinetics indicate that it is probably a saponin.

A unified biochemical and continuum mechanical red blood cell membrane bilayer--couple model.

We study the shapes and biochemical characteristics of human red blood cells using a unified biochemical and continuum mechanical model. In particular, we model the crenated, echinocytic shapes and show how they may shift due to changes in the pH and various amphipaths affecting the osmotic pressure by also utilizing pressure as an independent variable. In contrast to earlier works which advocate that biochemical factors may be attributable to mechanical control parameters, cytoskeletal elastic constants and effective relaxed bilayer area difference of outer plasma membrane and inner protein-based membrane skeleton, our unified model agrees well with Band 3 diffusion experimental root mean square distance data.

Effect of pH and temperature on the binding of bilirubin to human erythrocyte membranes.

Effect of pH and temperature on the binding of bilirubin to human erythrocyte membranes was studied by incubating the membranes at different pH and temperatures and determining the bound bilirubin. At all pH values, the amount of membrane-bound bilirubin increased with the increase in bilirubin-to-albumin molar ratios (B/As), being highest at lower pH values in all cases. Further, linear increase in bound bilirubin with the increase in bilirubin concentration in the incubate was observed at a constant B/A and at all pH values. However, the slope value increased with the decrease in pH suggesting more bilirubin binding to membranes at lower pH values. Increase in bilirubin binding at lower pH can be explained on the basis of increased free bilirubin concentration as well as more conversion of bilirubin dianion to monoanion. Temperature dependence of bilirubin binding to membranes was observed within the temperature range of 7 degrees -60 degrees C, showing minimum binding at 27 degrees C and 37 degrees C which increased on either side. Increase in bilirubin binding at temperatures lower than 20 degrees C and higher than 40 degrees C can be ascribed to the change in membrane topography as well as bilirubin-albumin interaction.

Modulation of bilayer fluidity by lipid peroxidation of human placental syncytiotrophoblast membranes during embryogenesis.

Placental syncytiotrophoblast while regulating the passage of nutrients from maternal blood to the fetal circulation exposes itself to the risk of oxidative attack by the oxygen free radicals. Extent of lipid peroxidation (LPO) investigated in placental brush border membrane (BBM) and basal membrane (BM) revealed a decreasing trend with gestational progress. Steady-state fluorescence anisotropy measurement of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labeled malondialdehyde treated placental membrane vesicles suggested modulation of BBM and BM fluidity by lipid peroxidation in all gestational ages. alpha-tocopherol content in both the placental membranes which increased as gestation progressed has been proposed to play a significant role in decreasing LPO of placental membranes during intrauterine development.

Antigen F1 from yersinia pestis forms aqueous channels in lipid bilayer membranes

Antigen F1 is a protein of 17 kDa produced by Yersinia pestis it is cultured at 37 grade C. When incorporated into planar lipid bilayer membranes this protein induces fluctuations on membrane conductance typical of the formation of ionic channels. These fluctuations reveal two distinct unitary conductance sizes, one in the range of 800 to 1400 pS and the other in the range of 140 to 600 pS. Zero current potential measaurements in the presence of a salt gradient show that the channell is not significantly ion selective. The reversal potential measured in the presence of 0.5 MKCl on the cis side and 0.1 MKCl on the trans side was 3.58 ñ 3.98 mV (N=7). The non-selectivity of the channel, in addition to its large conductance, suggests that it forms large aqueous pores. The present results, taken together with other data showing that nantigen F1 inhibits the activity of phagocytic cells, suggest that antigen F1 acts by forming aqueous pores in the membrane of these target cells

Membrane-associated cytoskeleton and transbilayer phospholipid asymmetry.

Earlier studies have suggested that the membrane-associated cytoskeleton (membrane skeleton) in erythrocytes plays a major role in maintaining the transmembrane phospholipid asymmetry. But recently, it has been proposed that an ATP-dependent aminophospholipid pump is the sole determinant of this asymmetry in these cells. A critical analysis of the published data along with some unpublished results from the author's laboratory, however, indicate that both membrane skeleton and ATP-dependent aminophospholipid pump are required for maintaining the membrane phospholipid asymmetry in native erythrocytes.