Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 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 investigated the energy requirement of mitochondrial protein import with a simplified system containing only isolated yeast mitochondria, energy sources and a purified precursor protein. This precursor was a fusion protein composed of 22 residues of the cytochrome oxidase subunit IV pre-sequence fused to mouse dihydrofolate reductase. Import of this protein required not only an energized inner membrane, but also ATP. ATP could be replaced by GTP, but not by CTP, TTP or non-hydrolyzable ATP analogs. Added ATP did not increase the membrane potential of respiring mitochondria; it supported import even if the proton-translocating mitochondrial ATPase and the entry of ATP into the matrix were blocked. We conclude that ATP exerts its effect on mitochondrial protein import outside the inner membrane.
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PMID:Both ATP and an energized inner membrane are required to import a purified precursor protein into mitochondria. 303 90