Mechanics of receptor ligand binding in immune cell synapses

Cell-surface receptors and ligands of the immune system bind each other during dynamic cell-cell contacts called immune synapses. Such interactions are important for immune recognition of foreing antigens, communication and transfer of material between cells, and spreading of pathogens. In contrast to soluble molecules, molecular interactions at cellular interfaces are influenced by the effects of the membrane environment, including passive and active mechanical forces, which can lead to modified receptor-ligand binding and unbinding rates and bond strengths, affecting the efficiency of molecular signalling events and specific cellular functions. In addition, many receptors are either organised in multivalent clusters or cluster upon ligand binding, which might lead to preferential receptor orientations or cooperative effects which could in turn influence the molecular binding mechanics. It is important to understand the specificity and potency of receptor-ligand systems, for instance, to elucidate the mechanisms of discrimination between self and non-self during cellular immune function, or to uncover the mechanisms of receptor-mediated virus entry.
Probing receptor-ligand bonds in situ has been a challenging task, but new force-sensing and force-pulling experiments at the single molecule level allow measurement of the relevant bond-rupture forces and kinetic binding rates under different force-loading conditions for various receptor-ligand systems.
This project will use single molecule biophysical mechanical assays to investigate synaptic binding of B cell antigen receptors to antigens and of HIV particles to their cellular receptors. Binding will be measured using optical and magnetic tweezers with particular focus on the effects of mechanical forces and valency. These experiments will be followed by functional characterisation of the binding properties in immune cell activation and viral infection.
The student will receive laboratory training in molecular biology and experimental biophysics. The student will learn single molecule force spectroscopy with optical and magnetic tweezers in cell free and cellular systems. The student will have the opportunity to interact closely with immunologists and cell biologists at the Crick and to learn varioius techniques of live cell microscopy. The student will also interact with physicists in the Dept. of Physics and Astronomy at UCL to receive training in microscopy development, programming for image processing, data analysis and hardware control. The student will attend scientific seminars and conferences relevant for the project and present experimental data in formal talks and research publications.
This project aligns with the current EPSRC grand challenge Understanding the Physics of Life and fits specifically in the Biophysics and Soft Matter Physics research area (Physical Sciences theme) in the EPSRC portfolio. It fits particularly in the named strategic areas of optical tweezers and single molecule microscopy/spectroscopy for the investigation of cellular processes and biological systems.
Project milestones:
Year 1: Expression of receptors and antigens, design of magnetic/optical tweezers experiments.
Year 2: Single molecule force-pulling experiments with magnetic/optical tweezers, measurents of binding in cell free and cellular systems.
Year 3-4: Functional effects of antigen binding on B cell activation and on the interactions of HIV with its receptors.
Resources and expertise:
Access to primary B cells, cell lines, cell culture, live cell imaging fluorescence microscopy and magnetic tweezers are avalilable in Tolar lab. In Tolar lab, the student will work closely with a postdoc who specialises in magnetic tweezer experiments in the lab.
Access to shared wet labs, experimental physics lab and an advanced platform for combined single molecule fluorescence microscopy and optical tweezers for force sensing are available in Llorente-Garcia lab.