Abstract

The tafazzin gene encodes a phospholipid-lysophospholipid transacylase involved in cardiolipin metabolism, but it is not known why it forms multiple transcripts as a result of alternative splicing. Here we studied the intracellular localization, enzymatic activity, and metabolic function of four isoforms of human tafazzin and three isoforms of Drosophila tafazzin upon expression in different mammalian and insect systems. When expressed in HeLa cells, all isoforms were localized in mitochondria except for the B-form of Drosophila tafazzin, which was associated with multiple intracellular membranes. Among the human isoforms, only full-length tafazzin (FL) and tafazzin lacking exon 5 (Delta5) had transacylase activity, and only these two isoforms were able to restore a normal cardiolipin pattern, normal respiratory activity of mitochondria, and male fertility in tafazzin-deficient flies. Both FL and Delta5 were associated with large protein complexes in 293T cell mitochondria, but treatment with alkali and proteinase K suggested that the Delta5 isoform was more integrated into the hydrophobic core of the membrane than the FL isoform. Although all Drosophila isoforms showed transacylase activity in vitro, only the A-form supported cardiolipin remodeling in flies. The data suggest that humans express two mitochondrial isoenzymes of tafazzin that have similar transacylase activities but different membrane topologies. Furthermore, the data show that the expression of human tafazzin in flies creates cardiolipin with a Drosophila pattern, suggesting that the characteristic fatty acid profile of cardiolipin is not determined by the substrate specificity of tafazzin.