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Artificial Transmembrane Signalling



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Cell membranes coordinate a large variety of biological processes by selectively recognising and responding to different external stimuli, and membrane-spanning proteins play a vital role in these signalling pathways. A large number of examples of synthetic membrane channels and transporters have been reported in the past four decades. However, signal transduction without mass transfer is considerably more challenging. In this dissertation, an indirect artificial transmembrane signalling mechanism which operates by controlled translocation of a synthetic transducer across the lipid bilayer was investigated. The fundamental concept of the translocation mechanism is the switching of membrane-permeability of the two head groups of the transducers. The recognition head group of the transducer becomes membrane-permeable in response to an external chemical stimulus, which leads to membrane translocation, exposing a catalytic head group to the interior of the vesicle. Catalytic hydrolysis of an internal substrate generates an amplified output signal. Previously reported examples showed that the transducer could respond to different external stimuli, such as pH (hydroxide ions) or metal ions. Herein, we present efforts towards generalising the concept and extending the scope of this mechanism into more biological systems. Firstly, a maleimide transducer was designed as a “stem transducer” to which a wide range of recognition groups could be attached in situ by using maleimide-thiol conjugation chemistry. Secondly, a carboxylic acid transducer was studied in an attempt to achieve controlled cargo-release in response to an acid input. Thirdly, a vesicle-to-vesicle communication system was assembled with a desthiobiotin transducer by leveraging the desthiobiotin-avidin-biotin system. This example represents a key step towards designing artificial cell-like compartments that communicate in a similar way to cells. Furthermore, we explored an analogue of the β-galactose transducer and the viability of using enzymatic cleavage as an input on the membrane surface. Finally, 19F NMR studies were conducted to provide insight into the positioning of the catalytic head groups of transducers in the membrane, and a fluorescence quenching assay was used to determine the ion transport ability of transducers. This work provides further understanding of the proposed membrane translocation mechanism and extends the scope of artificial transmembrane signal transduction from purely synthetic assemblies into more sophisticated biological systems. This opens up the potential for the future development of intelligent responsive vesicles in bionanotechnology.





Hunter, Christopher


Transmembrane Signalling, Signal Transduction, Cell Signalling, Membrane Translocation, Artificial Vesicles


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
EPSRC, Trinity College Cambridge, Department of Chemistry