Phospholipids are the building blocks of biological membranes. Membranes leverage the amphipathic chemistry of lipids to form bilayers that encapsulate a cell and its multitude of organelles. Such compartmentalization has enabled cells to separate biochemical pathways, establish specialized functions that can respond when appropriate, and adapt to constantly fluctuating metabolic conditions. The Claypool laboratory’s research focus is on the underappreciated contribution of the mitochondrion to cellular phospholipid metabolism. In addition to being the sole producer of the canonical mitochondrial lipid, cardiolipin (CL), the mitochondrion hosts one of the two major pathways in a cell for the production of phosphatidylethanolamine (PE). Ablation of the mitochondrial capacity to synthesize either CL or PE is embryonically lethal in mice. The mitochondrial pathway of PE production therefore provides a pool of this lipid that cannot be replaced by the other three PE biosynthetic pathways. Moreover, in the yeast Saccharomyces cerevisiae the combined absence of CL and PE is synthetically lethal. Thus, both CL and PE are crucial for mammalian development and have distinct and yet overlapping properties that are essential not only for mitochondrial function, but life itself.
The lab currently has two major ongoing projects centered on different aspects of mitochondrial phospholipid metabolism in health and disease.
CL and the ADP/ATP carrier interactome— Current estimates indicate that 1 in 5000 children will develop an oxidative phosphorylation (OXPHOS) disorder. The ADP/ATP carrier/Adenine nucleotide translocase (yeast AAC = mammalian ANT) mediates the 1:1 exchange of ADP into and ATP out of the mitochondrial matrix and is thus required for OXPHOS. Recently, we demonstrated that the major ADP/ATP carrier in the yeast S. cerevisiae, Aac2p, physically associates with the respiratory supercomplex but only in the context of mitochondrial membranes that contain cardiolipin. Our determination of a cardiolipin-dependent Aac2p interactome raises four critical questions: (1) do these AAC interactions subscribe to an evolutionarily conserved organizing principle? (2) what is the molecular basis for the cardiolipin-dependency? (3) how do these completely unexpected interactions contribute to normal mitochondrial function? and (4) what are the consequences when this network of interactions is disrupted?
Current Goals:1.To define the contribution of the mammalian ANT interactome for mitochondrial function.2.To determine at a molecular level the role of cardiolipin in establishing the ADP/ATP carrier interactome.3.To define how the Aac2p-respiratory supercomplex association contributes to mitochondrial function.
Funding: NIH – National Heart, Lung, and Blood Institute
Mitochondrial PE metabolism— Phosphatidylethanolamine (PE) is a non-bilayer forming phospholipid that is essential for life. Disruption of either of the two major PE-producing pathways, the CDP-ethanolamine pathway or the phosphatidylserine (PS) decarboxylase pathway, is embryonically lethal in mice. PS decarboxylase 1 (Psd1p) is an integral inner mitochondrial membrane protein that produces the vast majority of PE in the mitochondrion and can provide the entire cellular complement of PE in yeast. Very little is known about Psd1p’s mechanism and most of the lipid trafficking steps required for this pathway remain obscure. Further, exactly how PE produced in mitochondria supports mitochondrial function is incompletely resolved.
Current Goals:1.To define key structural motifs necessary for Psd1p activity.2.To determine the functional importance of producing PE in the mitochondrial inner membrane.3.To characterize the inter-organelle lipid trafficking steps.
Funding: NIH – National Institute of General Medical Sciences