Physics ABC Seminar: by Sonali Gandhi and Gobin Acharya, Wayne State University

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Date: October 20, 2020
Time: 3:30 p.m. - 4:30 p.m.
Location: Zoom
Category: Seminar

I. Fluorescence Cross-Correlation Spectroscopy (FCCS) to reveal the molecular mechanisms of lipolysis

Sonali Gandhi
Department of Physics and Astronomy, Wayne State University

The dynamics of lipids and proteins are crucial in the mechanisms of cellular functions. The interactions between proteins and lipids on the membrane surrounding lipid droplets regulates lipolysis and the digestion of triglycerides within the lipid droplet. In particular, we aim to develop novel methods for revealing the interactions between lipolysis-associated proteins, including adipose triglyceride lipase (ATGL), perilipin (PLIN), and alpha-beta hydrolase domain-containing protein 5 (ABHD5). In our current study, we apply fluorescence cross-correlation spectroscopy (FCCS) to study the interactions between these lipids and proteins. We use a super-continuum laser to excite the fluorescent proteins that diffuse through the diffraction-limited spot. The fluorescence emission is chromatically spread by a prism and collected by a sCMOS camera at 6 kHz. The intensity versus time of each color channel is extracted through a linear least-square fitting of each camera frame and temporally correlated. From the auto- and cross-correlation functions, we measure the diffusion rates and oligomerization of the proteins. To demonstrate the capabilities of our custom instrumentation, we use supported lipid bilayers (SLBs) to study the diffusion and cross-linking of membrane-bound cholera toxin subunit B. Our preliminary experiments show the hetero-oligomerization of ABHD5 and PNPLA3 on the ER of live COS7 cells. Our goal is to examine molecular-scale behaviors dependent on the phospholipid composition, PLIN associations, and protein concentrations in the presence of ligands. This study provides a further understanding of how lipolysis is regulated via protein interactions with the lipid membrane to regulate lipase activity.

II. Revealing the microscopic dynamics of nanoconfined water and ethanol in graphene oxide

Gobin Acharya
Department of Physics and Astronomy, Wayne State University

Water is the natural solvent as well as a major component of living beings which influences many biological activities. Ethanol is also an important fluid in chemical, biological and industrial processes. The purification of water and the separation of water and ethanol are important, but energy-intensive processes. Therefore, nanomaterials are being studied that may facilitate water and ethanol separation. One such material is graphene oxide (GO). When water and ethanol are confined in GO capillaries, their confinement can change the dynamic properties of the confined molecules. We utilized the momentum transfer (Q)-dependence of Quasi-Elastic Neutron Scattering (QENS) to reveal the dynamics and the almost isotropic behaviors of water and ethanol intercalated in GO at different temperatures. The microscopic dynamics of water and ethanol was probed and compared at different length and time scales and different temperatures by using several spectrometers. The results will be presented.



Zhi-Feng Huang




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