The export of proteins across the cytoplasmic membrane is an essential function for all cells. In bacteria, two distinct transport mechanisms are used: The well-studied Sec pathway transports unfolded proteins via extrusion through a membrane-bound channel. In contrast, much less is known regarding the Twin Arginine Translocation (Tat) pathway responsible for the transport of folded proteins. The complexity required for this function is beyond that of a simple conformational change, and requires the orchestration of multiple copies of multiple proteins assembled into a large protein complex.
We recently developed a new form of artificial lipid bilayer that in addition to exceptional stability, and simple reconstitution of membrane proteins, is capable of single-molecule fluorescence imaging and single-channel electrical recording with gigaohm seals. Droplet Interface Bilayers (DIBs) are created by contacting aqueous droplets in a lipid/oil solution. We propose to reconstitute the minimal components of the Tat system in Droplet Interface Bilayers to create a working in vitro model of this important biological pathway. Using this method we will exploit single-molecule imaging to dissect the individual steps of Tat-driven transport, and in particular quantify the changes in stoichiometry of the assembled complex that occur during transport.
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