Understanding Membrane Curvature Sensing
McMahon, Harvey T
University of Cambridge
MRC Laboratory of Molecular Biology
Doctor of Philosophy (PhD)
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Colussi, A. (2017). Understanding Membrane Curvature Sensing (Doctoral thesis). https://doi.org/10.17863/CAM.17212
Eukaryotic cells are characterised by membranes with varied and dynamic compositions and shapes. Consequently, membrane-binding proteins are tuned to recognise and modify these membrane states to perform their functions. To study the curvature sensitivity of proteins, I have developed a single-particle assay using NanoSight technology that tracks the Brownian motion of particles to measure their size. I optimised this system to track fluorescently labelled lipid-binding domains bound to liposomes of different sizes moving freely in solution. The comparison of the size distribution of the total liposomes with the fluorescently labelled population allowed me to determine their curvature preferences. To validate the method I tested proteins from the Bin/Amphiphysin/Rvs (BAR) superfamily, which are inherently curved and have known curvature preferences. My method was capable of recapitulating the behaviour of BAR domains with different curvature preferences. I then expanded the range of targets and showed that this assay is also capable of detecting curvature preferences for a variety of other lipid-binding domain families. As such, I identified AKT PH domain as a new curvature-sensing domain. Finally, using the ENTH domain of Epsin1 that causes vesicle budding, I demonstrated that this method can also be used to study membrane remodelling. Trafficking involves generation and sensing of membrane curvature combined with recognition of specific cargo. Endophilin consists of a curvature-sensitive BAR domain followed by an SH3 (Src-homology 3) domain and has recently been identified in a clathrin-independent endocytosis pathway, FEME (fast endophilin-mediated endocytosis), involved in the uptake of cell surface receptors. Endophilin recognises ligands via its SH3 domain, binding G-protein coupled receptors (GPCRs) directly in their intracellular loop 3 and receptor tyrosine kinase (RTKs) via adaptor proteins. However, a specific recognition motif has not been identified yet. Here, using a combination of biophysical approaches and NMR spectroscopy, I characterised the Endophilin binding motif of ALIX (ALG-2-interacting protein X) adaptor protein and of the GPCR $\alpha$2A adrenergic receptor. Comparison of SH3-peptide models resulted in a putative Endophilin recognition site.
membrane curvature, curvature sensing, Endophilin, endocytosis, clathrin-independent, BAR
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This record's DOI: https://doi.org/10.17863/CAM.17212
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