(593g) Evaluation of Transmembrane Proteins for Stabilizing Emulsions

The majority of surfactants in the industry are compounds synthesized from hydrocarbons and many of them are highly toxic to the environment. They can be difficult to degrade and their sub-products and synthesis process may generate a high environmental impact. Biosurfactants are produced by living cells and may substitute some of the surfactants synthesized by the petrochemical industry, contributing to the reduction of the release of pollutants and environmental risk. They are biodegradable, less toxic,non-hazardous, have better foaming properties, higher selectivity, and can be active at extreme temperatures, pH and salinity. Moreover, they can be produced from industrial wastes and by-products. These advantages demonstrate the importance of studying this type of surfactants and to produce it from biological origin. There are different industrial applications for the Biosurfactants, such as stabilizers of emulsions and surface active

The bacteria Escherichia coli contain large amounts of outer membrane protein in their membranes that can be used as biosurfactants. The Outer membrane protein X (OmpX) is an E. coli outer membrane protein, which is conformationally stable. The crystal structure of OmpX consists of eight all- next neighbor antiparallel -strands that fold into a cylindrical barrel with polar residues on the inside and hydrophobic residues on the outside facing the membrane environment. The height of the cylindrical barrel is approximately 32 A° and its diameter 20 A°, and four of the -strands extend out of the predicted membrane boundaries to a total height of 50 A°. The strands are connected by three loops on the perisplamic side. The structure and the stability of the OmpX in water-dodecane solution and in pure water are investigated by molecular dynamics simulations on the 3000 ns timescale. The crystal structure (Protein Data Bank (PDB) entry 1QJ9, resolution 2.1 Amstrong has been taken as the starting structure. The simulations allow the determination of protein-lipid mixed micelle and the calculation of the emulsion´s viscosity. Two different types of simulations of OmpX in water-dodecane are carried out: one type starts from the protein solvated in a box of TIP4 and the other starts from the OmpX solvated in water-dodecane mixture in a box of 6 x 6 x 6 nm³, using a Gromos 54 force field, the number of dodecane´s molecules added randomly is 75,92 which corresponds to the optimal percentage of lipids used in the industry . The system is equilibrated under conditions of NVT (300 K) and NPT; they are neutralized with NaCl molecules. Each simulation starts with an energy minimization. All MD simulations are carried out using the GROMACS 4 5 4.

In order to validate and compare the MD results experimentally, the OmpX is expressed with IPTG (2 mM), purified and then concentrated from the E. coli  K-12 ASKA library using heterologous expression and affinity chromatography. The OmpX expression is confirmed by SDS PAGE to finally determine the stability of  this protein in water - dodecane emulsions and evaluate the potential of the OmpX as biosurfactant