Anna Sundborger-Lunna, PhD
Assistant Professor & Section Leader
Cryo-EM and Molecular Cell Biology
University of Minnesota Hormel Institute
Masonic Cancer Center
801 16th Avenue NE
Austin, MN 55912
Tel: 507-437-9647
Email: asundbor@umn.edu

Membrane remodeling and cell fate In the Cryo-EM and Molecular Cell Biology Section we are studying how membrane-bending proteins assemble into large complexes and regulate fundamental membrane remodeling events, such as apoptosis, autophagy and mitochondrial dynamics. Our primary focus is to determine how dysregulation of these pathways contributes to infectious diseases and cancer. Equipped with a Titan Krios electron microscope (FEI) fitted with phase plates and a Falcon 3 direct electron detector, we are able to solve the 3D structure of key proteins and protein complexes at atomic resolution in the ultimate effort to identify key players that contribute to regulation of cell death and to identify novel drug targets.

There is a strong link between intracellular pathways that regulate cell death and cancer. Remodeling of cellular membranes is a key feature during these processes and there is emerging evidence that membrane remodeling BAR domain-containing proteins (BAR proteins) serve important tumor suppressor functions in the cell, though their exact mechanisms are unknown. BAR protein endophilin B1 is involved in the regulation of apoptosis, though the exact mechanisms are unclear.

Previous studies show that endophilin B1 promotes oligomerization of pro-apoptotic protein Bax. Bax is recruited to the outer mitochondrial membrane (OMM) where oligomerizes to form a pore, a process critical for apoptosis (figure 1). Knockdown of endophilin B1 in cells inhibits Bax-mediated apoptosis. Bax activity is regulated by BH3-only domain protein from the Bcl-2 family. Our hypothesis is that endophilin B1 promotes apoptosis by facilitating recruitment and activation of Bax at the OMM in a similar manner. Endophilin B1 also interacts with key regulators of autophagy, a pro-survival process, which suggests that endophilin B1 plays an important role in determining cell fate.

Our preliminary data shows that endophilin B1 preferentially binds to lipid membrane vesicles containing cardiolipin, a lipids enriched in the OMM required for Bax activation (figure 2).

(from left to right): Dr. Anna Sundborger, PI, Dr. Veer Bhat, Hormel Fellow, Nodir Boymatov, SURE student

We are currently collecting data of these endophilin B1-decorated lipid tubules in the Titan Krios and our goal is to generate a 3D reconstruction at atonic resolution that will shed insight into how endophilin B1 assembles on cardiolipin-enriched lipid membrane and further how it may regulate Bax assembly. We are also in the process purifying recombinant Bax from E.Coli. Upon completion, we will initiate experiments to determine the structural relationship between endophilin B1 endophilin B1 and Bax on cardiolipin-containing lipid vesicles. Endophilin B1-Bax assembles will be further characterized using cryo-EM.

Presentations

Gordon Conference “Three-Dimensional Electron Microscopy”
Les Diablerets, Switzerland

Department of Gastroenterology and Hepatology
Mayo Clinic, Rochester

Institute for Medical Virology
University of Minnesota, Minneapolis

Masonic Cancer Center
University of Minnesota, Minneapolis

Biophysical Society 58th Annual Meeting
New Orleans, LA

“Equipped with a Titan Krios electron microscope (FEI)
fitted with phase plates and a direct electron detector,
we are able to solve the 3D structure of key proteins and
protein complexes at atomic resolution, in the ultimate
effort to identify key players that contribute to regulation
of cell death and to identify novel drug targets.”
Dr. Anna Sundborger