A thermotropic behavior of egg PC liposome containing the very long chain fatty acyl component, ??,??-13,16-dimethyloctacosanedioate dimethyl ester (DME C30) isolated from the thermophilic anaerobic bacteria, Thermoanaerobacter ethanolicus

Thermoanaerobacter ethanolicus is a strictly anaerobic and thermophilic bacterium whose optimum temperature ranges over 65-68 ??C. T. ethanolicus was known to contain a bipolar very long chain fatty acyl component such as ??,??-13,16-dimethyloctacosanedioate as one of the major membrane components. However, exact physiological role of this unusual component in the membrane remains unknown. Such a very long chain fatty acyl component, ??,??-13,16-dimethyloctacosanedioate dimethyl ester (DME C30), was isolated, and purified from the membrane of T. ethanolicus. As a function of added concentrations of the ??,??-13,16-dimethyloctacosanedioate dimethyl ester (DME C30) or cholesterol into the standard liposomes, the acyl chain ordering effect was investigated by the steady-state anisotropy with 1,6-diphenyl-1,3,5-hexatriene (DPH) as a fluorescent probe. Acyl chain order parameter (S) of vesicles containing DME C30 is higher comparing with phosphatidylcholine (PC) only vesicles. This result was discussed thermodynamically with the aid of the simulated annealing molecular dynamics simulations. Through the investigation of all the possible conformational changes of DME C30 or cholesterol, we showed that DME C30 is very flexible and its conformation is variable depending on the temperature comparing with cholesterol, which is rigid and restricted at overall temperature. We propose that the conformational change of DME C30, not the configurational change, may be involved in the regulation of the membrane fluidity against the changes of external temperature.close3