Identification of the Yeast Mitochondrial Transporter for Oxaloacetate and Sulfate

Abstract

Saccharomyces cerevisiae encodes 35 members of the mitochondrial carrier family, including the OAC protein. The transport specificities of some family members are known, but most are not. Saccharomyces cerevisiae has two principal pathways for replenishing the intermediates of the Krebs cycle that have been withdrawn for biosynthesis. They are the glyoxylate cycle and the carboxylation of pyruvate to oxaloacetate, catalyzed by two cytosolic isozymes of pyruvate carboxylase. (Mammalian pyruvate carboxylase is in the mitochondrial matrix.) These processes require traffic of substrates across the inner mitochondrial membrane. S. cerevisiae encodes 35 members of the mitochondrial carrier family (1-4), including the dicarboxylate and succinate-fumarate carriers (5, 6). The former catalyzes the import into mitochondria of succinate (or malate) in exchange for phosphate, producing a net uptake of succinate and supply of a substrate to the Krebs cycle (7). The latter exchanges external succinate for fumarate and is required for gluconeogenesis (6,8). Yeast gene disruption strains (⌬-DIC1 and ⌬-SFC1) cannot grow on either ethanol or acetate as sole carbon source, but they grow well on glycerol, pyruvate and other nonfermentable substrates (7, 9). Growth of the ⌬-DIC1 strain on ethanol or acetate is restored by both low concentrations of oxaloacetate and other compounds that start the tricarboxylate cycle (and the oxidation of the acetyl-CoA unconsumed by the glyoxylate cycle) by generating either intramitochondrial oxaloacetate or other Krebs cycle intermediates (7). Therefore, does oxaloacetate enter yeast mitochondria, and if so, how?The S. cerevisiae gene OAC1 1 (formerly known as PMT or YKL120w) encodes a member of the mitochondrial carrier family of hitherto unknown function that is 29% identical to the yeast DIC, its closest relative in yeast and 30% identical to the bovine 2-oxoglutarate/malate carrier. OAC and the dicarboxylate carrier are the only carriers that cluster on a phylogenetic tree with the bovine oxoglutarate/malate carrier (10, 11). Disruption of the OAC1 gene produced no phenotype on rich glycerol medium (12), and its transcript level was higher in synthetic than in rich medium (13).We have overexpressed the OAC in E. coli, reconstituted it into phospholipid vesicles, and shown that it transports oxaloacetate, sulfate, and thiosulfate both in vitro and in vivo. One of its main functions is probably to carry oxaloacetate produced by cytoplasmic pyruvate carboxylase into the mitochondrial matrix.

The malate–aspartate NADH shuttle components are novel metabolic longevity regulators required for calorie restriction-mediated life span extension in yeast

“…In yeast, the existence and importance of the malate-aspartate shuttle has been debatable until the transporters required for the malate-aspartate shuttle to operate were identified (Palmieri et al 1996(Palmieri et al , 1999(Palmieri et al , 2001Cavero et al 2003). Here our data showed that the malate-aspartate shuttle played a major role in mediating life span extension under CR as well as in Multiple CR pathways act to affect longevity in yeast.…”

α-Isopropylmalate, a Leucine Biosynthesis Intermediate in Yeast, Is Transported by the Mitochondrial Oxalacetate Carrier

“…Oac1p transports oxalacetate into the yeast mitochondrial matrix with protons or by exchange with other substrates and operates with the same transport properties in vivo and in reconstituted liposomes (26). In the same study, it was suggested that the role of Oac1p is to take up into mitochondrial oxalacetate produced by pyruvate carboxylase, which in S. cerevisiae is only cytoplasmic.…”

“…In a previous study, Oac1p was shown to be the yeast mitochondrial transporter for oxalacetate and sulfate (26). Oac1p transports oxalacetate into the yeast mitochondrial matrix with protons or by exchange with other substrates and operates with the same transport properties in vivo and in reconstituted liposomes (26).…”

Identification and Functional Characterization of a Novel Mitochondrial Carrier for Citrate and Oxoglutarate in Saccharomyces cerevisiae

“…In addition, Yhm2p shares only 21 and 22% identical amino acids with Ctp1p and CTP, respectively. Yhm2p also differs from the dicarboxylate (38,39) and oxaloacetate (16,40) 1 from Plasmodium falciparum (31%) and XP_001238657.1 from Eimeria tenella (31%)), Euglenozoa (e.g. XP_811279.1 from Trypanosoma cruzi (32%)), and Stramenopiles (e.g.…”