Geranylgeranylated SCF^FBXO10 regulates selective outer mitochondrial membrane proteostasis and function.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Cellular membrane protein turnover, particularly at specific compartments like the outer mitochondrial membrane (OMM), remains poorly understood.
• The precise mechanisms governing protein localization and function within mitochondria are critical for cellular energy production and homeostasis.

Purpose of the Study:

• To elucidate the mechanism of FBXO10 targeting to the OMM.
• To investigate the role of FBXO10 in mitochondrial function and proteostasis.
• To identify substrates and downstream effects of FBXO10 activity.

Main Methods:

• Investigated protein lipid modification (geranylgeranylation) of FBXO10 at cysteine 953.
• Utilized protein interaction studies with cytosolic factors (PDE6δ, HSP90) for OMM targeting.
• Employed FBXO10 mutants (C953S) to assess mitochondrial function (ATP production, membrane potential, fragmentation).
• Applied comparative quantitative proteomics to identify mitochondrial substrates.
• Assessed effects on protein degradation (PGAM5), mitochondrial homeostasis, and myogenic differentiation in iPSCs and myoblasts.

Main Results:

• FBXO10 undergoes geranylgeranylation at C953, mediating its OMM localization via interaction with PDE6δ and HSP90.
• The FBXO10(C953S) mutant shows impaired OMM targeting, reduced mitochondrial ATP production, loss of membrane potential, and increased fragmentation.
• Phosphoglycerate mutase-5 (PGAM5) identified as an OMM-localized substrate of FBXO10.
• FBXO10 deficiency or a prenylation-deficient mutant inhibits PGAM5 degradation, disrupts mitochondrial homeostasis, and impairs myogenic differentiation.

Conclusions:

• Geranylgeranylation is a key mechanism for FBXO10 OMM targeting and function.
• FBXO10 regulates mitochondrial proteostasis through PGAM5 degradation, impacting cellular energy and differentiation.
• This pathway represents a potential therapeutic target for mitochondrial dysfunction.