Background:The phospholipid cardiolipin undergoes acyl chain remodeling after biosynthesis, which has been hypothesized to optimize mitochondrial function. Results: ⌬cld1 yeast, containing unremodeled cardiolipin, have no mitochondrial morphology or oxidative phosphorylation defects. Conclusion: Cardiolipin remodeling is not required for optimal mitochondrial bioenergetic function in yeast. Significance: Cardiolipin remodeling may be important for presently unknown mitochondrial processes and/or have unappreciated physiological functions.

Complexes containing tafazzin, which remodels newly synthesized cardiolipin, are destabilized by mutations associated with Barth syndrome.

Patients with Barth syndrome (BTHS), a rare X-linked disease, suffer from skeletal and cardiomyopathy and bouts of cyclic neutropenia. The causative gene encodes tafazzin, a transacylase, which is the major determinant of the final acyl chain composition of the mitochondrial-specific phospholipid, CL. In addition to numerous frame shift and splice-site mutations, 36 missense mutations have been associated with BTHS. Previously, we established a BTHS-mutant panel in the yeast Saccharomyces cerevisiae that successfully models 18/21 conserved pathogenic missense mutations and defined the loss-of-function mechanism associated with a subset of the mutant tafazzins. Here, we report the biochemical and cell biological characterization of the rest of the yeast BTHS-mutant panel and in so doing identify three additional modes of tafazzin dysfunction. The largest group of mutant tafazzins is catalytically null, two mutants encode hypomorphic alleles, and another two mutants are temperature sensitive. Additionally, we have expanded the defects associated with previously characterized matrix-mislocalized-mutant tafazzins to include the rapid degradation of aggregation-prone polypeptides that correctly localize to the mitochondrial IMS. In sum, our in-depth characterization of the yeast BTHS-mutant panel has identified seven functional classes of BTHS mutation.

Our understanding of the clinically relevant tafazzin-mediated cardiolipin (CL) remodeling pathway is incomplete. In this study, a new trafficking step required for CL remodeling has been identified. Further, it is demonstrated that flux through this CL remodeling pathway is controlled by the strength of the mitochondrial electrochemical gradient.

The mitochondrial phospholipid cardiolipin (CL) promotes bioenergetics via oxidative phosphorylation (OXPHOS). Three tightly bound CLs are evolutionarily conserved in the ADP/ATP carrier (AAC in yeast; adenine nucleotide translocator, ANT in mammals) which resides in the inner mitochondrial membrane and exchanges ADP and ATP to enable OXPHOS. Here, we investigated the role of these buried CLs in the carrier using yeast Aac2 as a model. We introduced negatively charged mutations into each CL-binding site of Aac2 to disrupt the CL interactions via electrostatic repulsion. While all mutations disturbing the CL-protein interaction destabilized Aac2 monomeric structure, transport activity was impaired in a pocket-specific manner. Finally, we determined that a disease-associated missense mutation in one CL-binding site in ANT1 compromised its structure and transport activity, resulting in OXPHOS defects. Our findings highlight the conserved significance of CL in AAC/ANT structure and function, directly tied to specific lipid-protein interactions.