Biochemical investigation of LC3/GABARAP-ligand interaction as an important quality measure for LC3/GABARAP-targeting small molecules: addendum to the guidelines (4th edition).

Targeted protein degradation (TPD) represents a new therapeutic modality that allows the targeting of proteins that are considered undruggable by conventional small molecules. While TPD approaches via the ubiquitin-proteasome system are well established and validated, additional degradation pathways still require rigorous characterization. Here, we focus on macroautophagy/autophagy tethering compounds, a class of small molecules, designed to recruit cargo to LC3/GABARAP proteins for subsequent autophagosome-dependent degradation. We provide guidance for the biophysical and structural characterization of small molecule modulators for studying LC3/GABARAP-ligand interactions. In addition, we discuss potential limitations of autophagy-based TPD systems and emphasize the need for rigorous quality control in the development of LC3/GABARAP-targeting small molecules.Abbreviations: DSF: differential scanning fluorimetry; FP: fluorescence polarization; FRET: Förster/fluorescence resonance energy transfer; HTRF: homogeneous time-resolved fluorescence; ITC: isothermal titration calorimetry; LIR: LC3-interacting region; MGs: molecular glues; NMR: nuclear magnetic resonance; PROTACs: PROteolysis-TArgeting Chimeras; SPR: surface plasmon resonance; TPD: targeted protein degradation; TR-FRET: time-resolved Förster/fluorescence resonance energy transfer; UPS: ubiquitin-proteasome system.