Faculty Bibliography

Tafazzin is a transacylase that affects cardiolipin fatty acid composition and mitochondrial function. Mutations in human tafazzin cause Barth syndrome yet the enzyme has mostly been characterized in yeast. To study tafazzin in higher organisms, we isolated mitochondria from Drosophila and mammalian cell cultures. Our data indicate that tafazzin binds to multiple protein complexes in these organisms, and that the interactions of tafazzin lack strong specificity. Very large tafazzin complexes could only be detected in the presence of cardiolipin, but smaller complexes remained intact even upon treatment with phospholipase A2. In mammalian cells, tafazzin had a half-life of only 3-6h, which was much shorter than the half-life of other mitochondrial proteins. The data suggest that tafazzin is a transient resident of multiple protein complexes.

In addition to specific intermolecular interactions, biological processes at membranes are also modulated by the physical properties of the membrane. One of these properties is membrane curvature. NMR methods are useful for studying how membrane curvature affects the binding and insertion of proteins into membranes as well as how proteins can affect membrane curvature properties. In many cases these interactions result in a marked change in protein activity. We have reviewed examples from a range of systems having varied mechanisms by which membrane curvature is linked to protein activity. Among the examples discussed are antimicrobial peptides, proteins affecting membrane fusion, rhodopsin, protein kinase C, phospholipase C-delta1, phosphatidylinositol-3 kinase-related kinases and tafazzin. This article is part of a Special Issue entitled: NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces.

Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes. Indeed, cardiolipin is a universal component of mitochondria in all eukaryotes. It has a unique dimeric structure comprised of two phosphatidic acid residues linked by a glycerol bridge, which gives rise to unique physicochemical properties. Cardiolipin plays an important role in the structural organization and the function of mitochondrial membranes. In this article, we review the literature on cardiolipin biology, focusing on the most important discoveries of the past decade. Specifically, we describe the formation, the migration, and the degradation of cardiolipin and we discuss how cardiolipin affects mitochondrial function. We also give an overview of the various phenotypes of cardiolipin deficiency in different organisms.

The dynamical behavior of mitochondria has attracted much attention, but little is known about the dynamics of mitochondrial lipids, specifically cardiolipin (CL). Here, we estimated the turnover of select molecular species of CL in mammalian cell cultures and compared it to the turnover of other lipids, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol. Cells were labeled with myristic acid, 9,10-(2)H2-oleic acid, or d-[U-(13)C6]-glucose and analyzed by mass spectrometry at different time points of pulse-chase experiments. The turnover of glycerol groups was monitored by specific isotopologues that carried (13)C primarily in the glycerol carbons, whereas the turnover of acyl groups was monitored by molecular species that carried myristoyl or (2)H2-oleoyl groups. We found that the turnover of CL, but not of mitochondrial PC and PE, was substantially slower than the turnover of other cellular phospholipids. In dioleoyl-PC and dioleoyl-PE, the acyl turnover was faster than the glycerol turnover, indicating continuous deacylation and reacylation of the oleoyl residues. In contrast, the acyl turnover was similar to the glycerol turnover in tetraoleoyl-CL, suggesting that oleoyl remodeling did not take place continuously in endogenous CL. We conclude that CL, once assembled in mitochondrial membranes, remains largely inert to degradation and acyl remodeling.

The idea of a Cardiolipin workshop in Italy came to the meeting organizers in June 2011, during the mini-sabbatical of Angela Corcelli in New York City in the Laboratory of Michael Schlame. They thought to take advantage of the presence of the 54th International Conference on the Bioscience of Lipids (ICBL) at Bari in 2013 to organize the Cardiolipin workshop as a satellite event. The web page of the Cardiolipin Meeting was kindly supported by the Euro Fed Lipid organization. About 60 scientists attended the meeting focused on the multiple roles of cardiolipin in mitochondria in physiological and pathological states in various organisms as well as in bacterial membranes. In addition to ICBL participants, many students and colleagues of the Universities of Bari and Lecce attended the meeting, increasing the number of total participants to about 100. As defects in cardiolipin metabolism may cause Barth syndrome, the meeting also presented an occasion to establish contacts between the nascent Italian Barth Syndrome Foundation and scientists actively involved in cardiolipin research. C1 [Corcelli, Angela] Univ Bari A Moro, Dept Basic Med Sci Neurosci & Sensory Organs, Bari, Italy. [Schlame, Michael] NYU, Sch Med, New York, NY USA

Cardiolipin, the specific phospholipid of mitochondria, is involved in the biogenesis, the dynamics, and the supramolecular organization of mitochondrial membranes. Cardiolipin acquires a characteristic composition of fatty acids by post-synthetic remodeling, a process that is crucial for cardiolipin homeostasis and function. The remodeling of cardiolipin depends on the activity of tafazzin, a non-specific phospholipid-lysophospholipid transacylase. This review article discusses recent findings that suggest a novel function of tafazzin in mitochondrial membranes. By shuffling fatty acids between molecular species, tafazzin transforms the lipid composition and by doing so supports changes in the membrane conformation, specifically the generation of membrane curvature. Tafazzin activity is critical for the differentiation of cardiomyocytes, in which the characteristic cristae-rich morphology of cardiac mitochondria evolves. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

Cardiolipin is a mitochondrial phospholipid with a characteristic acyl chain composition that depends on the function of tafazzin, a phospholipid-lysophospholipid transacylase, although the enzyme itself lacks acyl specificity. We incubated isolated tafazzin with various mixtures of phospholipids and lysophospholipids, characterized the lipid phase by (31)P-NMR and measured newly formed molecular species by MS. Substantial transacylation was observed only in nonbilayer lipid aggregates, and the substrate specificity was highly sensitive to the lipid phase. In particular, tetralinoleoyl-cardiolipin, a prototype molecular species, formed only under conditions that favor the inverted hexagonal phase. In isolated mitochondria, <1% of lipids participated in transacylations, suggesting that the action of tafazzin was limited to privileged lipid domains. We propose that tafazzin reacts with non-bilayer-type lipid domains that occur in curved or hemifused membrane zones and that acyl specificity is driven by the packing properties of these domains.