Ggc1p is a yeast mitochondrial carrier protein involved in the GTP/GDP transport. This protein encoded by YDL198c gene has been shown to be a multicopy suppressor (by an unknown mechanism) of the ability of the abf2 null mutant to grow at 37°C on glycerol. The ABF2 gene whose product is involved in mitochondrial genome maintenance in S. cerevisiae. Abf2Δ cells loose mtDNA at a high rate when grown in glucose medium and show a temperature-sensitive defect on non-fermentable carbon sources. The physiological role of Ggc1p in S. cerevisiae is the GTP transport into mitochondria, in exchange for intramitochondrially generated GDP. In addition, ggc1Δ cells exhibit lower levels of GTP and increased levels of GDP in their mitochondria; they are unable to grow on nonfermentable substrates, and they loose mtDNA. In the mitochondrial matrix, GTP is required as an energy source for protein synthesis; as a substrate for the synthesis of tRNA, mRNA, rRNA, and RNA primers; and as a phosphate group donor for the activity of GTP-AMP phosphotransferase and G proteins. In several organisms, GTP is synthesized in the mitochondria by succinyl-CoA ligase, which catalyzes the conversion of succinyl-CoA to succinate with the generation of GTP, and by nucleoside diphosphate kinase, which catalyzes the transfer of the phosphate from ATP to a nucleoside diphosphate, to yield nucleotide triphosphates. In S. cerevisiae, however, succinyl-CoA ligase produces ATP instead of GTP, and the mitochondrial nucleoside diphosphate kinase is localized in the intermembrane space and it is absent in the matrix. These observations imply that in S. cerevisiae GTP has to be imported into the mitochondria probably via a carrier system embedded in the inner mitochondrial membrane. Here, this protein has been overexpressed in E. coli, reconstituted into phospholipid vesicles, and tested for a variety of potential substrates. When citrate is present, the carrier changes the transport activity, from an antiport mechanism to an uniport mechanism. A similar response has also been observed for the protein in the mitochondria. We conclude that uniport transport of GTP is involved in the homeostasis of guanine nucleotide pool in the mitochondrial matrix.
Unidirectional transport of the mitochondrial GTP/GDP carrier in Saccharomyces cerevisiae
VILLALOBOS COA, VALENTINA LOIRA;MAROBBIO, CARLO MARYA;VOZZA, Angelo
2015-01-01
Abstract
Ggc1p is a yeast mitochondrial carrier protein involved in the GTP/GDP transport. This protein encoded by YDL198c gene has been shown to be a multicopy suppressor (by an unknown mechanism) of the ability of the abf2 null mutant to grow at 37°C on glycerol. The ABF2 gene whose product is involved in mitochondrial genome maintenance in S. cerevisiae. Abf2Δ cells loose mtDNA at a high rate when grown in glucose medium and show a temperature-sensitive defect on non-fermentable carbon sources. The physiological role of Ggc1p in S. cerevisiae is the GTP transport into mitochondria, in exchange for intramitochondrially generated GDP. In addition, ggc1Δ cells exhibit lower levels of GTP and increased levels of GDP in their mitochondria; they are unable to grow on nonfermentable substrates, and they loose mtDNA. In the mitochondrial matrix, GTP is required as an energy source for protein synthesis; as a substrate for the synthesis of tRNA, mRNA, rRNA, and RNA primers; and as a phosphate group donor for the activity of GTP-AMP phosphotransferase and G proteins. In several organisms, GTP is synthesized in the mitochondria by succinyl-CoA ligase, which catalyzes the conversion of succinyl-CoA to succinate with the generation of GTP, and by nucleoside diphosphate kinase, which catalyzes the transfer of the phosphate from ATP to a nucleoside diphosphate, to yield nucleotide triphosphates. In S. cerevisiae, however, succinyl-CoA ligase produces ATP instead of GTP, and the mitochondrial nucleoside diphosphate kinase is localized in the intermembrane space and it is absent in the matrix. These observations imply that in S. cerevisiae GTP has to be imported into the mitochondria probably via a carrier system embedded in the inner mitochondrial membrane. Here, this protein has been overexpressed in E. coli, reconstituted into phospholipid vesicles, and tested for a variety of potential substrates. When citrate is present, the carrier changes the transport activity, from an antiport mechanism to an uniport mechanism. A similar response has also been observed for the protein in the mitochondria. We conclude that uniport transport of GTP is involved in the homeostasis of guanine nucleotide pool in the mitochondrial matrix.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
