COX11 (cytochrome c oxidase copper chaperone COX11) functions as an essential assembly factor for mitochondrial respiratory chain complex IV (cytochrome c oxidase) 1. The protein acts as a metallochaperone that specifically delivers copper to the copper B site of COX1, facilitating proper complex IV assembly and function 1. COX11 is critical for maintaining cellular ATP production through oxidative phosphorylation, as demonstrated by studies showing that COX11 knockdown significantly decreases cellular ATP levels derived from respiration 2. Interestingly, these ATP deficits can be restored by coenzyme Q10 supplementation, suggesting COX11 has broader roles in mitochondrial energy metabolism beyond direct complex IV assembly 2. The protein localizes to mitochondria and shows evolutionary conservation from yeast to humans 3. Disease-wise, biallelic pathogenic variants in COX11 cause infantile-onset mitochondrial encephalopathies, classified as mitochondrial complex IV deficiency nuclear type 23 24. Additionally, alternative splicing of COX11 mediated by PTBP3 affects copper homeostasis and cellular sensitivity to cuproptosis, with implications for cancer progression 5. COX11 expression levels also correlate with patient outcomes in various cancers, including colorectal cancer where low expression associates with poor prognosis 6.