Molecular Studies on FUNDC2 a candidate gene for mitochondrial diseases.

Human chromosome Xq28 is a gene-rich region, which lies within the critical linkage interval for many human diseases and characterized by an unusual degree of genomic instability. Here we report the structural/functional analysis of a new Xq28 gene FUNDC2 that encodes for a small mitochondrial protein with unknown function. The gene maps approximately 4,1 kb centromeric to F8 and 6,5 kb telomeric to MTCP1. Comparative and chromosomal mapping indicates that FUNDC2 has duplicated to specific locations near the pericentromeric region of human chromosomes highlighting a phenomenon for paralogous genome evolution common to other Xq28 genes. FUNDC2 has ubiquitously expression in human embryos and adult tissues with high level in the heart and skeletal muscle. Its predicted protein shows high conservation from Archeabacteria to Human suggesting that it could be a member of a new family of functionally related genes. Its 189-amino-acid sequence appears rich of hydrophobic residues and lacks a signal-sequence for protein sorting or target membrane. In HeLa and COS cells, confocal immuno-fluorescence studies co-localized FUNDC2 protein to the mitochondria stained by anti-HSP60 antibody and pECFP-mito. We also performed subcellular fractionation by differential centrifugation and alkali treatment establishing that FUNDC2 is located in the mitochondria inner membrane. Based on a high-throughput yeast 2-hybrid screen, we found that Drosophila FUNDC2 orthologue interacts with mtacp1 (mitochondrial acyl carrier protein 1. Its human counterpart is NDUFAB1, a subunit of the mitochondrial respiratory Complex I that is the entry point for electrons donated from NADH. Mutations in the structural building blocks of Complex I have been detected in 40% of patients with Complex I deficiencies. Further investigation of FUNDC2 will contribute to understanding of its function as well as provide a new candidate for mitochondrial pathogenesis including those associated to Complex I deficiency.