ABSTRACT
In this issue of Molecular Cell, Tsutsui et al. (2015) show that in vivo protein crystallization may come in handy not only when solving the structure of a protein, but also when studying molecular mechanisms of selective autophagy.
Subject(s)
Anthozoa/chemistry , Cytosol/metabolism , Green Fluorescent Proteins/chemistry , Lysosomes/metabolism , Animals , HumansABSTRACT
Mitophagy, the selective removal of damaged or excess mitochondria by autophagy, is an important process in cellular homeostasis. The outer mitochondrial membrane (OMM) proteins NIX, BNIP3, FUNDC1, and Bcl2-L13 recruit ATG8 proteins (LC3/GABARAP) to mitochondria during mitophagy. FKBP8 (also known as FKBP38), a unique member of the FK506-binding protein (FKBP) family, is similarly anchored in the OMM and acts as a multifunctional adaptor with anti-apoptotic activity. In a yeast two-hybrid screen, we identified FKBP8 as an ATG8-interacting protein. Here, we map an N-terminal LC3-interacting region (LIR) motif in FKBP8 that binds strongly to LC3A both in vitro and in vivo FKBP8 efficiently recruits lipidated LC3A to damaged mitochondria in a LIR-dependent manner. The mitophagy receptors BNIP3 and NIX in contrast are unable to mediate an efficient recruitment of LC3A even after mitochondrial damage. Co-expression of FKBP8 with LC3A profoundly induces Parkin-independent mitophagy. Strikingly, even when acting as a mitophagy receptor, FKBP8 avoids degradation by escaping from mitochondria. In summary, this study identifies novel roles for FKBP8 and LC3A, which act together to induce mitophagy.
Subject(s)
Microtubule-Associated Proteins/genetics , Mitophagy , Tacrolimus Binding Proteins/genetics , Ubiquitin-Protein Ligases/metabolism , HeLa Cells , Humans , Membrane Proteins/genetics , Membrane Proteins/metabolism , Microtubule-Associated Proteins/metabolism , Mitochondrial Membranes/metabolism , Mitochondrial Proteins/metabolism , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Proto-Oncogene Proteins c-bcl-2/genetics , Proto-Oncogene Proteins c-bcl-2/metabolism , Saccharomyces cerevisiae/metabolism , Tacrolimus Binding Proteins/metabolism , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/metabolism , Two-Hybrid System TechniquesABSTRACT
The covalent conjugation of ubiquitin-fold modifier 1 (UFM1) to proteins generates a signal that regulates transcription, response to cell stress, and differentiation. Ufmylation is initiated by ubiquitin-like modifier activating enzyme 5 (UBA5), which activates and transfers UFM1 to ubiquitin-fold modifier-conjugating enzyme 1 (UFC1). The details of the interaction between UFM1 and UBA5 required for UFM1 activation and its downstream transfer are however unclear. In this study, we described and characterized a combined linear LC3-interacting region/UFM1-interacting motif (LIR/UFIM) within the C terminus of UBA5. This single motif ensures that UBA5 binds both UFM1 and light chain 3/γ-aminobutyric acid receptor-associated proteins (LC3/GABARAP), two ubiquitin (Ub)-like proteins. We demonstrated that LIR/UFIM is required for the full biological activity of UBA5 and for the effective transfer of UFM1 onto UFC1 and a downstream protein substrate both in vitro and in cells. Taken together, our study provides important structural and functional insights into the interaction between UBA5 and Ub-like modifiers, improving the understanding of the biology of the ufmylation pathway.