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Invariant BECN1 C‐x‐x‐C Motifs Are Essential For Starvation‐Induced Autophagy

Autophagy is an essential catabolic cellular homeostasis process conserved in all eukaryotes. BECN1, a protein essential for autophagosome nucleation, contains two invariant C‐x‐x‐C motifs (18CxxC21 and 137CxxC140 in human BECN1) that bookend a large BECN1 intrinsically disordered region (IDR). We use circular dichroism spectroscopy to elucidate differences in secondary structural content of the wild‐type and CysTetrad mutant BECN1 IDR. Additionally, we are using small angle X‐ray scattering analyses to further understand the impact of the CysTetrad mutation on the structure of the BECN1 IDR. We also show that helicity of the BECN1 IDR increases upon addition of 2,2,2‐trifluoroethanol (TFE), suggesting that it may undergo binding‐associated helical transitions. Further, we use ICP‐MS to demonstrate that BECN1 binds Zn2+ in a 1:1 molar ratio under both, reducing and non‐reducing environments. Lastly, we show that both C‐x‐x‐C motifs are required, while the IDR is also important, for starvation‐triggered up‐regulation of autophagy.