Proteins are embedded in model "membranes" of tunable interlamellar distance separation d. To get precise insights on their interaction, we measure the evolution of protein lateral diffusion D versus d. For large d values lateral interaction between proteins diffusing within the same membrane could be observed whereas for intermediate d values proteins in opposite membranes could also interact.
Our system was calibrated by a well-documented interaction between streptavidin and a biotinated transmembrane peptide. From the variation of D(d) we are able to specify the configuration adopted, the stoichiometry and the binding energy of the formed complex.
We then studied proteins which form an efflux pump across the double membrane of Pseudomonas Aeruginosa bacteria. Our results demonstrate the interaction of proteins belonging to opposite membranes and we calculate the stoichiometry of the formed complex. The results obtained corroborate crystallographic data.
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