Brian Sun
Program: Electrical & Systems Engineering
Current advisor: Matthew D. Lew, PhD
Undergraduate university: Washington University
Research summary
I am currently an MD/PhD student in Professor Matthew Lew’s lab. I engineer optical imaging hardware, software, and fluorescent probes to investigate how the conformations and orientations of biological structures (e.g. viral surface proteins, amyloid-beta fibrils) affect their biophysical properties and interactions. My goal is to understand how these conformational dynamics modulate disease pathogenesis and cellular responses to infection.
One of the imaging technologies I am currently developing is a computational pipeline that can precisely estimate fluorescent probe orientations in rapidly changing biological environments. I will ultimately apply this pipeline, in combination with polarization-sensitive microscopes, to image the orientational dynamics of cell membranes during processes such as vesicular exo- and endocytosis and conformational changes in membrane proteins during ligand binding.
Throughout Phase 1, I also worked with Professor Lew to understand the growth and decay of amyloid-beta fibrils using single-molecule orientation localization microscopy (SMOLM). A-beta, as a biomarker of ailments like Alzheimer’s Disease, is of great interest to researchers who seek to understand how its elusive growth and decay mechanisms influence disease progression. However, existing imaging modalities cannot uncover the nanoscale processes driving these remodeling dynamics. SMOLM, as a super-resolution imaging technique that can measure the 3D position and orientation of individual fluorescent molecules on biological structures, is well-equipped to glean new insights into A-beta’s growth and decay mechanisms by probing the fibrils’ underlying beta-sheet structures. In my project, I applied SMOLM to establish that well-aligned, stable beta sheets tend to correspond to stable A-beta fibrils, with more dynamic beta sheets corresponding to decaying and growing structures. I also used SMOLM to discover and quantify various growth and decay mechanisms invisible to diffraction-limited imaging modalities; for example, an A-beta fibril’s beta-sheet structure can reorganize drastically without the fibril changing its overall shape. In totality, my study uses nanoscale structural measurements to paint a nuanced picture of A-beta growth and decay, hopefully informing our future understanding and treatment of neurodegeneration.
Prior to joining the Lew Lab, I rotated in the Vahey and Piston labs, where I gained wet-lab experience and investigated other interesting biological questions:
During my first rotation in the Vahey Lab, I worked with graduate student Yuanyuan He and Professor Michael Vahey to study how the properties of influenza A proteins influence the virus’s susceptibility to antibody inhibition. Understanding the biophysics of antibody-epitope (i.e. antibody binding site) interactions can inform the development of more potent influenza vaccines. To accomplish this goal, I learned and applied fluorescence recovery after photobleaching (FRAP) imaging to establish an inverse relationship between the stability of hemagglutinin (HA), an influenza A viral membrane protein, and the inhibition potency of FluA-20, a broadly neutralizing influenza A antibody.
During my second rotation in the Piston Lab, I investigated the diffusion and clustering behavior of Ephrin A4 (EphA4) receptors. Cell-cell communication through EphA4 receptors plays a central regulatory role in insulin and glucagon secretion from cells in the islet of Langerhans, and the membrane dynamics underpinning EphA4 cell-cell communication is consequently of great interest. To better understand these dynamics, I worked with staff scientist Dr. Alessandro Ustione to learn how to quantify EphA4 protein diffusion on cells using fluorescence correlation spectroscopy (FCS). I also learned wet lab techniques to purify protein plasmids from bacterial cultures and transfect cells with these plasmids for FCS imaging.
Graduate publications
Sun B, Ding T, Zhou W, Porter TS, Lew MD. 2024 Single-Molecule Orientation Imaging Reveals the Nano-Architecture of Amyloid Fibrils Undergoing Growth and Decay. Nano Lett, ():Online ahead of print.