TOMM70 is a member of the TOM complex that transports cytosolic pre-proteins destined for the mitochondrial compartments (reviewed in Sokol AM et al. 2014; Kreimendahl S & Rassow J 2020). The C-terminal tetratricopeptide repeat (TPR) motifs in TOMM70 recognizes the internal mitochondrial targeting signals (MTSs) of mitochondrial protein precursors in the cytosol and mediates their translocation to the mitochondria (reviewed in Sokol AM et al. 2014; Kreimendahl S & Rassow J 2020). The molecular chaperone complexes of heat shock protein 90 kDa (HSP90) and HSP70 bind to the N-terminal TPR clamp domain of TOMM70 and thus facilitate delivery of precursor proteins to TOMM70 (Young JC et al. 2003; Zanphorlin LM et al. 2016). Further, TOMM70 is involved in the activation of antiviral immunity by interacting with the mitochondrial antiviral signaling protein (MAVS) (Liu XY et al. 2010). Association of TOMM70 with MAVS is thought to promote the recruitment and activation of TBK1 and IRF3 to MAVS upon viral infection (Liu XY et al. 2010). Cryo?electron microscopy (cryo-EM) structure of the TOMM70:SARS-CoV-2 9b complex suggests that viral 9b binds to the substrate recognition site of TOMM70 thus competing with substrate proteins involved in the induction of type I IFN synthesis (Jiang HW et al. 2020; Gordon DE et al. 2020a; reviewed in Kreimendahl S & Joachim Rassow J 2020). Structural and biochemical analysis revealed that Ser53 of the viral 9b protein and Glu477 of TOMM70 are crucial for the association of both proteins and recruitment of HSP90 (Gao X et al. 2021; Brandherm L et al. 2021). Circular dichroism experiments and differential scanning calorimetry showed that the 9b:TOMM70 complex is more thermally stable than free TOMM70 (Ayinde KS etal. 2022). Isothermal titration calorimetry (ITC) showed that a synthetic peptide harboring a central segment of 9b binds TOMM70 with nanomolar KD (Gao X et al. 2021). Further, the binding affinity between the C-terminal EEVD motif of HSP90 and the N-terminal TPR clamp domain TOMM70 was decreased when TOMM70 was associated with viral 9b (Gao X et al. 2021). These data suggest that SARS-CoV-2 9b (ORF9b) interaction with TOMM70 inhibits binding of HSP90 to TOMM70.

This Reactome event shows binding of SARS-CoV-2 9b to TOMM70.