RT Journal Article SR Electronic T1 COA5 has an essential role in the early stage of mitochondrial complex IV assembly JF Life Science Alliance JO Life Sci. Alliance FD Life Science Alliance LLC SP e202403013 DO 10.26508/lsa.202403013 VO 8 IS 3 A1 Tang, Jia Xin A1 Cabrera-Orefice, Alfredo A1 Meisterknecht, Jana A1 Taylor, Lucie S A1 Monteuuis, Geoffray A1 Stensland, Maria Ekman A1 Szczepanek, Adam A1 Stals, Karen A1 Davison, James A1 He, Langping A1 Hopton, Sila A1 Nyman, Tuula A A1 Jackson, Christopher B A1 Pyle, Angela A1 Winter, Monika A1 Wittig, Ilka A1 Taylor, Robert W YR 2025 UL https://www.life-science-alliance.org/content/8/3/e202403013.abstract AB Pathogenic variants in cytochrome c oxidase assembly factor 5 (COA5), a proposed complex IV (CIV) assembly factor, have been shown to cause clinical mitochondrial disease with two siblings affected by neonatal hypertrophic cardiomyopathy manifesting a rare, homozygous COA5 missense variant (NM_001008215.3: c.157G>C, p.Ala53Pro). The most striking observation in the affected individuals was an isolated impairment in the early stage of mitochondrial CIV assembly. In this study, we report an unrelated family in whom we have identified the same COA5 variant with patient-derived fibroblasts and skeletal muscle biopsies replicating an isolated CIV deficiency. A CRISPR/Cas9-edited homozygous COA5 knockout U2OS cell line with a similar biochemical profile was generated to interrogate the functional role of the human COA5 protein. Mitochondrial complexome profiling pinpointed a role of COA5 in early CIV assembly, more specifically, its involvement in the stage between MTCO1 maturation and the incorporation of MTCO2. We therefore propose that the COA5 protein plays an essential role in the biogenesis of MTCO2 and its integration into the early CIV assembly intermediate for downstream assembly of the functional holocomplex.The mass spectrometry proteomics data for label-free whole-cell proteomics and complexome profiling produced in this study have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository (Perez-Riverol et al, 2022) and assigned the dataset identifier PXD050891 and PXD053461, respectively.