Professor Nate Wittenberg of Lehigh University

In my seminar, I will describe how my group uses model membrane systems, such as liposomes, supported lipid bilayers (SLBs), giant unilamellar vesicles (GUVs), and synthetic lipid droplets to study a variety of biological phenomena. Recently, we used SLBs and liposomes to investigate membrane-membrane interactions governed by the binding of myelin-associated glycoprotein (MAG) to ganglioside lipids.1 MAG is expressed on myelin in the nervous system, and it is one of the proteins responsible for crucial myelin-neuron interactions. Our model of the myelin-neuron interface consisted of SLBs decorated with MAG to mimic the myelin and liposomes rich in GT1b and GD1a gangliosides to mimic the neuronal membrane. Using quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence microscopy, we determined interaction kinetics and affinities for MAG-ganglioside interactions. We also show that monoclonal antibodies, similar to those present in Guillain-Barré syndrome, as well as cholesterol in the ganglioside-rich liposomes can inhibit MAG-ganglioside interactions.

I will also describe how we create high-density nanoarrays of liposomes and bacterial outer membrane vesicles, with the goal characterizing particle heterogeneity.2 Traditional ensemble assays reveal only average properties of these particles, which can obscure biologically-relevant distributions of size, surface biomarkers, and cargo. Using liftoff nanocontact printing, we define a nanoarray of capture spots, where each spot can capture a single particle. By capturing particles with biochemical specificity and packing them together tightly on a surface, our approach maximizes the number of particles per unit area while maintaining single particle optical resolution. We also used this method to capture, with biochemical specificity, individual outer membrane vesicles produced by two different strains of gram-negative bacteria

Finally, I will describe our results on the interplay between lipid oxidation and membrane curvature.3 Exposing a planar SLB possessing a photosensitizer to visible light results in the generation of highly-curved membrane nanotubes that transition into small vesicular structures. The formation of membrane nanotubes is caused by an area expansion of the lipid molecules that results from their photooxidation, and these nanotubes have diameters that are similar to those of tunneling nanotubes between cells. These results show that localized oxidative stress can have significant effects on membrane structure. We have also shown that lipid photooxidation significantly alters the interactions between liposomes and solid surfaces making them much more susceptible to rupture.4

References:
1. J.L. Cawley, L.R. Jordan, N.J. Wittenberg. Detection and Characterization of Vesicular Gangliosides Binding to Myelin-Associated Glycoprotein on Supported Lipid Bilayers. Analytical Chemistry 2021, 93, 1185-1192.
2. J.L. Cawley, M.E. Blauch, S.M. Collins, J.B. Nice, Q. Xie, L.R. Jordan, A.C. Brown, N.J. Wittenberg. Nanoarrays of Individual Liposomes and Bacterial Outer Membrane Vesicles by Liftoff Nanocontact Printing. Small 2021, 17, 2103338.
3. A.M. Baxter, L.R. Jordan, M. Kullappan, N.J. Wittenberg. Tubulation of Supported Lipid Bilayer Membranes Induced by Photosensitized Lipid Oxidation. Langmuir 2021, 37, 5753-5762.
4. A.M. Baxter, N.J. Wittenberg. Excitation of Fluorescent Lipid Probes Accelerates Supported Lipid Bilayer Formation via Photosensitized Lipid Oxidation. Langmuir 2019, 35, 11542-11549.