Integrin αIIbβ3: from platelet membrane to biomimetic models
Gaul, Vincent (2016) Integrin αIIbβ3: from platelet membrane to biomimetic models. PhD thesis, Dublin City University.
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The cell membrane is complex mixture of phospholipids, sphingolipids, sterols and proteins that combine to provide a semi-permeable barrier between the extracellular and intracellular environments, while also providing a functional role in cell-signalling, cell adhesion, and membrane transport. This complexity means that it is often better to study both the lipid and protein constituents of the cell membrane using artificial membrane models. Here, the transmembrane protein integrin αIIbβ3 was used as a model protein to be reconstituted into physiologically-relevant artificial lipid systems. αIIbβ3 is an integral membrane protein found in platelets and is a key mediator of thrombosis. Upon activation αIIbβ3 undergoes significant
conformational rearrangement, clustering, and ligand-binding to enable complex bidirectional signalling. It is this structural rearrangement, aggregation and ligand
binding that was the key focus of this project.
In chapter 2, and before reconstitution into artificial lipid models, αIIbβ3 was first studied in its native environment, the platelet. Here, DTT and Mn2+ were used to induce the activated form of αIIbβ3. It was found that both activators lead to structural changes in the integrin protein and varying degrees of platelet
aggregation, without the full range of response normally associated with physiological agonists. Chapter 3 focused on the production of αIIbβ3-reconstituted liposomes. It was found that integrin-ligand binding lead to a reduction in αIIbβ3 mobility, as well as integrin clustering. αIIbβ3 was also found to preferentially
excluded from cholesterol rich regions of lipid vesicles. Chapter 4 focused on the insertion of αIIbβ3 into a novel, cavity-spanning, lipid bilayer. Here, it was possible to determine αIIbβ3 diffusion co-efficients and induce protein aggregation. Finally, in chapter 5, cytoskeletal mimics were incorporated alongside a supported lipid bilayer in order to better imitate the conditions encountered by the cell membrane.
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