University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Thursday, September 12th 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Chiranjib Banerjee, University of Minnesota
Subject: Quantitative super-resolution analysis of ULK1 oligomeric states and cellular localization

Autophagy is a complex biological process that degrades and recycles cellular components. The induction of autophagy involves complex formation and membrane association of various regulatory proteins. However, the underlying molecular processes at a nanoscopic length scale remain enigmatic. Here, we combine quantitative super-resolution microscopy with endogenous tagging to study the oligomeric states and subcellular localization of ULK1, the protein kinase that plays a central role in autophagy induction. Our results reveal with single-molecule sensitivity that ULK1 exists as a distribution of oligomers with up to 50 molecules in nutrient-rich condition. In the amino-acid deficient condition, however, ULK1 first forms dense oligomeric clusters with nearly 100 molecules. These clusters then transition to loosely bound spherical oligomeric structures with radii between 100 nm and 400 nm without any further increase in the number of ULK1 molecules. Co-localization of ULK1 with its interaction partner ATG13 confirms that the ULK1 oligomers are implicated in the autophagy initiation process. Therefore, a critical number of ULK1 molecules is required to initiate autophagy. The dense clusters are in close proximity to the ER while the larger loosely bound structures are located further away from the ER. Moreover, the larger spherical structures are also co-localized with the phagophore marker LC3B which suggests that ULK1 also participates in the late stage of autophagy as well. This single molecule image analysis demonstrates the dynamic changes of autophagy initiation proteins at an unprecedented level of resolution.

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