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ABSTRACT: Mesenterocin 52A (Mes 52A) is a class IIa bacteriocin produced by Leuconostoc mesenteroides ssp. mesenteroides FR52. The interaction of Mes 52A with bacterial membranes of sensitive, resistant and insensitive Leuconostoc strains has been investigated. The degree of insertion of Mes 52A on the phospholipid bilayer was studied by fluorescence anisotropy measurements using two probes, 1-(4-trimethylammonium)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and DPH, located at different positions in the membrane, and the consequence for K(+) efflux and proton motive force was analyzed. Mes 52A caused an increase in the fluorescence of TMA-DPH and DPH in the membrane of the sensitive strain L. mesenteroides ssp. mesenteroides LMA 7, indicating that Mes 52A inserts into the cytoplasmic membrane of this sensitive strain. This insertion leads to K(+) efflux, without perturbation of DeltapH and a weak modification of DeltaPsi, and is consistent with pore formation. With the high-level resistant strain L. mesenteroides ssp. mesenteroides LMA 7AR, or with the insensitive strain Leuconostoc citreum CIP 103405, no modification of TMA-DPH or DPH anisotropy occurred, even in the presence of high Mes 52A levels. The membrane potential was not modified and no K(+) efflux was detected. There is a clear correlation between the physico-chemical characteristics of the membrane, the degree of Mes 52A penetration, the mechanism of action and the resistance or insensitivity characteristic of the target strains.
FEMS Microbiology Letters 12/2008; 289(2):193-201. · 2.04 Impact Factor
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ABSTRACT: Mesenterocin 52A (Mes 52A) is a class IIa bacteriocin produced by Leuconostoc mesenteroides subsp. mesenteroides FR52, active against Listeria sp. The interaction of Mes 52A with bacterial membranes of two sensitive Listeria strains has been investigated. The Microbial Adhesion to Solvents test used to study the physico-chemical properties of the surface of the two strains indicated that both surfaces were rather hydrophilic and bipolar. The degree of insertion of Mes 52A in phospholipid bilayer was studied by fluorescence anisotropy measurements using two probes, 1-(4-trimethylammonium)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and DPH, located at different positions in the membrane. TMA-DPH reflects the fluidity at the membrane surface and DPH of the heart. With Listeria ivanovii CIP 12510, Mes 52A induced an increase only in the TMA-DPH fluorescence anisotropy, indicating that this bacteriocin affects the membrane surface without penetration into the hydrophobic core of the membrane. No significant K(+) efflux was measured, whereas the Delta Psi component of the membrane potential was greatly affected. With Listeria innocua CIP 12511, Mes 52A caused an increase in the fluorescence of TMA-DPH and DPH, indicating that this peptide inserts deeply in the cytoplasmic membrane of this sensitive strain. This insertion led to K(+) efflux, without perturbation of Delta pH and a weak modification of Delta Psi, and is consistent with pore formation. These data indicate that Mes 52A interacts at different positions of the membrane, with or without pore formation, suggesting two different mechanisms of action for Mes 52A depending on the target strain.
Applied Microbiology and Biotechnology 10/2008; 81(2):339-47. · 3.42 Impact Factor
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ABSTRACT: Sphingomyelin pathway has been linked with insulin signaling through insulin-dependent GLUT-4 glucose transporter, but a relationship between sphingomyelin and the GLUT-1 transporter responsible for the basal (insulin-independent) glucose transport has not been clearly established. As GLUT-1 is mainly distributed to the cell surface, we explored the effects of changes in membrane sphingomyelin content on glucose transport through GLUT-1. The addition of exogenous sphingomyelin or glutathione (an inhibitor of endogenous sphingomyelinase) to the culture medium increased membrane sphingomyelin and cholesterol contents. Basal glucose uptake was enhanced and positively correlated to sphingomyelin (SM), cholesterol (CL) and SM/CL ratio. The exposure of 3T3-L1 preadipocytes to sphingomyelinase (SMase) significantly increased basal glucose uptake, membrane fluidity and decreased membrane sphingomyelin and cholesterol contents 60 min after SMase addition. There was no significant change in the abundance of GLUT-1 at the cell surface. The membrane sphingomyelin and cholesterol contents, fluidity and basal glucose transport returned to baseline levels within 2 h. The basal glucose uptake was negatively correlated with cholesterol contents and positively with SM/CL ratio. The SM/CL ratio might represent an important parameter controlling basal glucose uptake and a mechanism by which insulin resistance might be induced.
Cellular Signalling 12/2003; 15(11):1019-30. · 4.06 Impact Factor
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ABSTRACT: The complex mechanisms by which obesity predisposes to insulin resistance are not clearly understood. According to a cell membrane hypothesis of insulin resistance, the defects in insulin action could be related to changes in membrane properties. The purpose of this work was to examine the relationship between 2 markers of insulin resistance (fasting plasma insulin [FPI] and homeostasis model assessment [HOMA IR]) and erythrocyte membrane lipid composition. In the first cross-sectional study, 24 premenopausal nondiabetic overweight women (body mass index [BMI], 32.5 +/- 0.9 kg/m(2); age, 35.7 +/- 2.2 years) were compared to 21 lean healthy women (BMI, 21 +/- 0.4 kg/m(2); age, 35.4 +/- 2.2 years). The second study examined whether a 3-month diet-induced weight loss, which usually improves insulin resistance, could also affect the membrane phospholipid (PL) composition and fluidity in the overweight group. Overweight women had significantly higher FPI levels (P <.0001), HOMA IR (P <.0001), membrane sphingomyelin (SM) (P <.05), and cholesterol (P <.05) contents than lean women. Baseline FPI and HOMA IR were positively correlated with membrane SM (P <.005), phosphatidylethanolamine (PE) (P <.005), and phosphatidylcholine (PC) (P <.05) contents, and negatively with phosphatidylinositol (PI) (P <.05) contents in the whole population. Multivariate regression analyses showed that 2 membrane parameters, PE and SM, were among the independent predictors of FPI or HOMA IR in the whole population, but also in the lean and the obese groups separately. Intervention induced a significant reduction in body weight (-5.7% +/- 0.7%), fat mass (-11.3% +/- 1.4%), and FPI (-10.2% +/- 5.4%). An improvement in membrane lipid composition was only observed in the insulin resistant subgroup (FPI > 9.55 mU/L). The reduction in FPI or HOMA IR was directly associated with reduction in SM and PE contents, a finding independent of the reduction in fat mass. A stepwise multiple regression analysis indicated that the changes in SM accounted for 26.6% of the variance in the changes in FPI as an independent predictor, with the changes in fat mass and PE as other determinants (27.8% and 20%, respectively, adjusted r(2) =.704, P <.0001). These results suggest that the abnormalities in the membrane PL composition could be included in the unfavorable lipid constellation of obesity which correlated with impaired insulin sensitivity.
Metabolism 10/2002; 51(10):1261-8. · 2.66 Impact Factor
