Daniel Arno Blum

• Proteins are usually classified as water-soluble proteins or membrane proteins based on their cellular localization. In the course of their biogenesis, there is a significant number of initially water-soluble proteins and, after crossing into the membrane, develop their actual function as pore-forming or receptor proteins. Although the passage of the water-soluble proteins into the membrane and the associated refolding of the proteins are essential steps for the formation of the protein functions, only a few high-resolution methods exist to investigate these individual steps of the protein-membrane binding and the simultaneous development of the final active conformation in the membrane. In this study the transition of some proteins from the aqueous phase into the functional integral membrane form is examined for two cases, the human peroxisomal targeting signal 1 (PTS1) receptor hsPEX5 and the presynaptic pore-forming neu-rotoxins (LaTXs) found in the venom of Latrodectus spiders, namely α-LCT, δ-LIT and α-LTX. A vertical and horizontal artificial bilayer setup was used, enabling simultaneous and sequential high-resolution electrical and fluorescent measurements at the single-molecule level. It is presented that hsPEX5 alone harbors the ability to interact with the artificial mem-brane and generate a conductive membrane-pore. The electrophysiological results revealed for the LaTXs the essential role of calcium in stabilizing the oligomerized pore and moreover the significance of the latrotoxin-channels in cellular calcium homeostasis.