A hybrid model to study pathological mutations of the human ADP/ATP carriers.

The adenine nucleotide carrier (Ancp) plays an essential role in the metabolism of cellular energy by catalyzing the transport of ADP and ATP across the inner mitochondrial membrane. Previous reports have indicated that mutations in the HANC1 gene, encoding the muscle isoform of human Ancp (HAnc1p), are directly involved in several diseases, including autosomal dominant progressive external ophthalmoplegia and cardiomyopathies. In this work, we studied three pathogenic HANC1 mutations at the biochemical level. To do so, we expressed the DdANCA gene, encoding the unique Ancp carrier of Dictyostelium discoideum (DdAncAp), in a yeast strain lacking all endogenous ANC genes. Our results indicate that DdAncAp is a good model for the human protein. It allows the carrier to be studied in yeast, and provides information on how the HANC1 mutations impair ADP/ATP transport in humans. A94D, A126D and V291M mutations, corresponding to A90D, A123D and V289M in HAnc1p, respectively, did not affect levels of DdAncAp in yeast mitochondria. However, while the wild-type DdAncAp fully restored growth of the ANC-null yeast strain on a non-fermentable carbon source, the carriers encompassing either the A94D or the A126D mutation failed to complement the null strain. The effect of the V291M mutation was not as pronounced, but led to impairment mainly of the nucleotide translocation process per se. These findings provide new insights into the mechanisms responsible for the diseases induced by HAnc1p mutations.