J Biol Chem. 2025 Dec 17. pii: S0021-9258(25)02922-9. [Epub ahead of print] 111070
COX6B1 is a nuclear-encoded subunit of the human mitochondrial cytochrome c oxidase (cIV) located in its intermembrane space-facing region. The relevance of COX6B1 in mitochondrial physiopathology was highlighted by the missense pathogenic variants associated with cIV deficiency. Despite the assigned COX6B1 role as a late incorporation subunit, the COX6B1 human cell line knock-out (KO) exhibited a total loss of cIV. To get a deeper insight into the mechanisms driving the lack of cIV assembly or destabilization in the absence of COX6B1, we used the COX6B1 KO cell background to express alternative oxidase and COX6B1 pathogenic variants. These analyses uncovered that the COX6B1 subunit is indispensable for redox-sensitive early cIV assembly steps, besides its contribution to the stabilization of cIV in the late assembly stages. In addition, we have evidenced the incorporation of partially assembled cIV modules directly into supercomplex structures, supporting the 'cooperative assembly' model for respiratory chain biogenesis.
Keywords: COX; COX6B1; COX6B2; OXPHOS assembly; alternative oxidase; cIV; complex IV; cytochrome c oxidase; mitochondrial deficiency; respiratory chain supercomplexes