Date of Award

8-31-2022

Document Type

Thesis (Ph.D.)

Department or Program

Chemistry

First Advisor

Michael J Ragusa

Abstract

All cells undergo stress throughout their lifetime, including single-celled bacterium or a single cell from a plant or a human. This stress can result in damage that can be detrimental to the cell if it is not removed. Thus, healthy cells require a tight balance between clearing damaged cellular material and its replenishment. Autophagy is a highly conserved process evolved by cells to encapsulate damaged material in a double membrane vesicle for its delivery to the lysosome (in mammals) or the vacuole (in yeast). Upon lysosomal delivery, the contents are degraded and returned to the cell for reuse. Autophagy can occur selectively in which specific cargo such as a damaged organelle is selectively targeted for degradation, or non-selectively where random cytosolic content is degraded. Critical to a type of selective autophagy and enhancing the efficiency of non-selective autophagy is a protein Atg23. However, little is known about Atg23’s function in this highly important cellular process.

Despite its identification in the early 2000s, little is known regarding the structure and function of Atg23. Furthermore, investigations had been previously limited to subcellular experiments with no recorded biochemical studies. This thesis utilizes several structural and biophysical techniques including x-ray crystallography, cryoEM, and small angle x- ray scattering to demonstrate that Atg23 is a highly elongated homodimer. We also characterize Atg23 as both an Atg9- and membrane-binding protein, where the latter interaction is mediated through electrostatics. Lastly, this work sheds light on the functional role of Atg23 as a membrane tether involved in clustering Atg9 vesicles prior to their transport to the autophagy initiation site.

Original Citation

Leary, K.A and Ragusa, M.J. (2022). Characterization of Protein-Membrane Interactions in Yeast Autophagy. Cells, 11 (12), 1876.

Hawkins, W.D., Leary, K.A., Andhare, D., Popelka, H., Klionsky, D.J, Ragusa, M.J. (2022). Dimerization-dependent membrane tethering by Atg23 is essential for yeast autophagy. Cell Reports, 39, 3: 110702.

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