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Liposomes, Exosomes, and Virosomes: From Modeling Complex
Membrane Processes to Medical Diagnostics and Drug Delivery
Monday Speaker Abstracts
18
Fluorescence-free Imaging and Tracking of Individual Secretory and Transmembrane
Proteins in a Living Cell
Matthew P. McDonald
, Katharina König, André Gemeinhardt, Richard W. Taylor, Susann
Spindler, Vahid Sandoghdar.
Max Planck Institute for the Science of Light, Erlangen, Bavaria, Germany.
The cellular membrane plays a pivotal role in many biological and medical processes. As an
example, proteins protruding from the membrane serve as signaling centers to nearby cells and
extracellular biomolecules. Intercellular communications and secretions are also mediated by the
membrane through endosome-membrane fusion. Here, we present our recent efforts towards
understanding this ubiquitous dynamic system. Using a novel optical interferometric scattering
detection technique (iSCAT), we observe real-time secretion events of single label-free proteins
ejected from a living cell. Importantly, iSCAT functions by way of mixing the weak analyte’s
scattering signature with a relatively strong reflected plane wave. Even the tiniest nanoparticles
are, therefore, observed via the interference between these two signals. In addition, we perform
analogous measurements to track gold nanoparticle labeled transmembrane proteins and lipids in
three dimensions as they diffuse across living cells and giant unilamellar vesicles. Temporal and
spatial resolutions of ~50 µs and ~1 nm are routinely achieved, allowing for an unprecedented
look into membrane-protein diffusion dynamics. The developed method thus has the potential to
solve a wide range of problems in cellular physiology, such as intercellular signaling,
immunology, and cancer malignancy.