Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.14 (ATP synthase)
 7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied the import into isolated yeast mitochondria of three hydrophobic passenger proteins attached to the N-terminal cleavable presequence of mitochondrial ATPase subunit 9 from Neurospora crassa. One natural precursor (pN9) contained N. crassa subunit 9; two chimaeric precursors, N9L/Y8-1 and N9L/Y9-2, respectively contained yeast mitochondrial ATPase subunits 8 and 9. In the absence of urea, pN9 and N9L/Y8-1 are imported efficiently but N9L/Y9-2 is not imported. After pretreatment of precursors in 4 M urea, binding of pN9 to mitochondria is marginally affected while its import is substantially inhibited; the binding to mitochondria of chimaeric proteins, N9L/Y8-1 and N9L/Y9-2, is greatly enhanced but no import is observed. This behaviour of import precursors containing hydrophobic passenger proteins is contrasted with that of a hydrophilic chimaeric precursor pCOXIV-DHFR, whose binding and import are enhanced by pretreatment with a high concentration of urea (8 M). The import of N9L/Y8-1 is very sensitive to the presence of low concentrations of urea in the import reaction mixture, and is abolished above 0.5 M urea although precursor binding to mitochondria is increased. By contrast, neither the import nor binding of pCOXIV-DHFR is affected directly by urea up to 0.8 M. These deleterious effects of urea on import of the chimaeric precursors N9L/Y8-1 and N9L/Y9-2 are interpreted in terms of a non-productive binding of these precursors to mitochondria, brought about by exposure of their hydrophobic domains resulting from urea unfolding. The generalization that membrane translocation of mitochondrial import precursors is enhanced by their prior unfolding in urea thus does not apply in the case of these precursors containing hydrophobic passenger proteins.
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PMID:Import into mitochondria of precursors containing hydrophobic passenger proteins: pretreatment of precursors with urea inhibits import. 216 55

We have utilized a homologous cell-free mitochondrial protein import system derived from the yeast Saccharomyces cerevisiae, in addition to performing a series of in vivo experiments in yeast, to investigate the coupling between cytosolic protein synthesis and protein transport into mitochondria. We found that the import of bulk mitochondrial proteins was inhibited in both the homologous in vitro reaction and in vivo upon arrest of cytosolic protein synthesis with the addition of cycloheximide. Tight coupling of synthesis and import was also demonstrated in vivo for the beta subunit of the mitochondrial F1-ATPase. We also investigated the effect of the antifolate methotrexate on the import of a fusion protein consisting of the mitochondrial targeting signal of yeast cytochrome oxidase subunit IV fused to mouse dihydrofolate reductase (the COXIV-DHFR fusion protein). Methotrexate has previously been shown to inhibit posttranslational import of COXIV-DHFR by preventing the DHFR moiety from unfolding. However, we found that antifolate addition had no inhibitory effect on the import of COXIV-DHFR in vivo, suggesting that its import into mitochondria in yeast cells occurs cotranslationally. Further, when we treated yeast with the proton ionophore carbonyl cyanide m-chlorophenylhydrazone to collapse the mitochondrial membrane potential and induce the accumulation of extramitochondrial precursor pools, we found that the ability to be imported by a strictly posttranslational mechanism upon reestablishing the membrane potential varied from one precursor to another, suggesting that cotranslational import may be mandatory for the import of some proteins in vivo. In summary, our findings are entirely consistent with the notion that import of proteins into yeast mitochondria occurs cotranslationally under normal conditions in vivo.
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PMID:Coupling of cytosolic protein synthesis and mitochondrial protein import in yeast. Evidence for cotranslational import in vivo. 838 May 82

We investigated the effect of L and D enantiomers of a 25-residue peptide derived from the N-terminal region of the presequence of Nicotiana plumbaginifolia F1beta subunit of the ATP synthase, pF1beta(1, 25), on import into spinach leaf mitochondria. Three in vitro synthesized precursor proteins using different import pathways were used. Import of the precursor proteins of F1beta subunit of the ATP synthase, pre-F1beta, and the alternative oxidase, pre-AOX, required addition of external ATP. whereas the chimeric precursor containing the N-terminal 84 amino acids of the cytochrome b2 precursor protein linked to dihydrofolate reductase, pre-b2(1, 84)-DHFR was not dependent on ATP. Import of pre-F1beta, and pre-AOX was inhibited already at 1 microM and 3 microM concentration of the L and D enantiomers, whereas inhibition of import of pre-b2(1, 84)-DHFR, occurred at concentrations >10 microM of both enantiomers. Binding efficiency of the precursor proteins was not affected by addition of the L and D enantiomers. There was no correlation between inhibition of import of pre-F1beta and pre-AOX and dissipation of membrane potential measured as a decrease of Rhodamine 123 fluorescence quenching. The inhibitory effect of the L and D presequence enantiomers on import of pre-F1beta and pre-AOX was concluded to occur within the outer membrane translocase machinery beyond the initial precursor receptor interaction. Furthermore, the fact that the D enantiomer had the same effect as the natural peptide showed that interaction of the presequence with the import machinery was not dependent on chiral properties of the presequence.
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PMID:L and D presequence peptides derived from the precursor of F1beta subunit of the ATP synthase inhibit mitochondrial protein import by interaction with import machinery. 1178 42