Structural basis and regulation of the reductive stress response

Abstract

Highlights d CUL2 FEM1B recognizes reduced FNIP1 through two interface zinc ions d Zn 2+ is essential for reductive stress signaling d FNIP1 access to CUL2 FEM1B is gated by BEX protein pseudosubstrate inhibitors d Mutation of FEM1B and BEX deletion cause similar developmental syndromes

How the ends signal the end: Regulation by E3 ubiquitin ligases recognizing protein termini

“…A structure with the substrate FNIP1 shows that Cys- and His-rich sequences of both FEM1B and FNIP1 co-chelate zinc atoms at the E3-substrate interface. This interaction is regulated by redox state, with FEM1B targeting FNIP1 for degradation as a part of reductive stress pathways ( Manford et al., 2021 ; Manford et al., 2020 ).…”

E3 ligase ligand chemistries: from building blocks to protein degraders

“…An important finding for the development of novel ligands targeting FEM1B was the importance of cysteine 186 for the recognition of substrates, including key substrate FNIP1. 298,299 Based on this knowledge and vast experiences in covalent ligand screening platforms, the Rape and Nomura groups performed a fluorescence-based screen of a cysteine-reactive library of 566 compounds. From this screening, a drug-like fragment EN106 (Example 113, Scheme 50) containing chloroacetamide warhead was discovered, 300 which inhibited association between a fluorescently labeled FNIP1 degron and FEM1B with an IC 50 value of 2.2 mM.…”

Emerging Link between Tsc1 and FNIP Co-Chaperones of Hsp90 and Cancer

“…Recent work has shown that reductive stress promoted the degradation of FNIP1, but not FNIP2 [ 36 ]. The mechanism was traced to the chelation of Zn 2+ by two reduced Cys residues in FNIP1, which recruits CUL2 FEM1B [ 36 , 37 ], the scaffold and recognition subunits of an E3-ubiquitin ligase complex [ 38 ]. Degradation of FNIP1 in this context promotes AMPK-PGC1α-mediated mitochondrial biogenesis to counteract reductive stress [ 36 , 37 ].…”

“…The mechanism was traced to the chelation of Zn 2+ by two reduced Cys residues in FNIP1, which recruits CUL2 FEM1B [ 36 , 37 ], the scaffold and recognition subunits of an E3-ubiquitin ligase complex [ 38 ]. Degradation of FNIP1 in this context promotes AMPK-PGC1α-mediated mitochondrial biogenesis to counteract reductive stress [ 36 , 37 ]. Interestingly, loss of FEM1B led to decreased lactate production [ 36 ], perhaps as a byproduct of FNIP1-dependent stabilization of FLCN and its recently described tumor suppressive effect on lactate dehydrogenase A [ 39 ].…”