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Project 5: Cellular entry and novel membrane probes

Project overview

This project aims to establish conceptually innovative approaches to cross membrane barriers and enter cells. The chemistry of cell-penetrating poly(disulfide)s (CPDs) that can grow directly on substrates of free choice for covalent delivery, represent an attractive option that has been exploited and is steadily maturing: important breakthroughs in the sidechain, terminator and initiator engineering have been achieved. Following uptake, these CPDs depolymerize to minimize toxicity and liberate the substrates in an unmodified form. Thus, the covalent delivery of broad range of substrates from the NCCR network is explored via proteomics, including proteins (antibodies, etc.), bicyclic peptides, quantum dots, probes such as SNAP-tags, or siRNA, and conceptually innovative CPD activators are developed.

New methods such as templated side-chain exchange are another center of interest to find the most powerful poly(disulfide) transporters: the combination of cell-penetrating poly(disulfide)s with biotin–streptavidin biotechnology has been achieved to provide for a simple, general, non-toxic method that avoids significant endosomal capture and delivers proteins directly, even to the nucleoli. This project is furthermore complemented by ongoing, more advanced studies on cell-penetrating dynamic amphiphilic peptide and dendrons hybrid macromolecules for the delivery of oligonucleotides like siRNA and plasmids.

Emphasis is also given on novel membrane probes including molecules such as planarizable push-pull probes, ceramide mimics and protein-based probes. Notably, planarizable push-pull probes explore, for the first time, the molecular principles of the color change of lobsters upon cooking or the chemistry of vision.

To image biologically important properties of biomembranes represent the 2nd main theme of this project. The detection of membrane tension is so far difficult to achieve but the chemical and biological approaches present in the labs involved in the project have the potential to solve this problem. Namely, the “fluorescent flippers”, a new concept that allows to insert large and bright monomers into oligomeric probes to really feel the environment and also shine when twisted out of conjugation, are studied to maximize mechanosensitivity and to be used to study the mechanism of TORC2 activation in vivo.

Other topics of interest include the sensing of membrane phases and microdomains (“rafts”) and also membrane potentials. In addition, new methods focusing on free-standing lipid bilayers not supported and named “electrofluorescent imaging” and compressible Langmuir monolayers (2D system model of biomembranes) are developed to comprehensively characterize new and old fluorescent membrane probes.