Gene/Protein Disease Symptom Drug Enzyme Compound
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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

A combination of atovaquone and proguanil has been found to be quite effective in treating malaria, with little evidence of the emergence of resistance when atovaquone was used as a single agent. We have examined possible mechanisms for the synergy between these two drugs. While proguanil by itself had no effect on electron transport or mitochondrial membrane potential (DeltaPsim), it significantly enhanced the ability of atovaquone to collapse DeltaPsim when used in combination. This enhancement was observed at pharmacologically achievable doses. Proguanil acted as a biguanide rather than as its metabolite cycloguanil (a parasite dihydrofolate reductase [DHFR] inhibitor) to enhance the atovaquone effect; another DHFR inhibitor, pyrimethamine, also had no enhancing effect. Proguanil-mediated enhancement was specific for atovaquone, since the effects of other mitochondrial electron transport inhibitors, such as myxothiazole and antimycin, were not altered by inclusion of proguanil. Surprisingly, proguanil did not enhance the ability of atovaquone to inhibit mitochondrial electron transport in malaria parasites. These results suggest that proguanil in its prodrug form acts in synergy with atovaquone by lowering the effective concentration at which atovaquone collapses DeltaPsim in malaria parasites. This could explain the paradoxical success of the atovaquone-proguanil combination even in regions where proguanil alone is ineffective due to resistance. The results also suggest that the atovaquone-proguanil combination may act as a site-specific uncoupler of parasite mitochondria in a selective manner.
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PMID:A mechanism for the synergistic antimalarial action of atovaquone and proguanil. 1034 48

The antisense method is one of the most promising anti-cancer methods, however, the design of antisense oligonucleotides is difficult because many factors affecting their activitiy and stability must be considered. Recently, the oligonucleotide stabilities related to the antisense effects were quantitatively investigated based on nearest-neighbor parameters. We demonstrated that DeltaG(o) (37, hyb), a free energy change for the hybridization of antisense oligodeoxynucleotides (ODNs) with target RNAs is related to the RNase H cleavage of TAg (SV40 large T antigen) mRNA, the expression of a rabbit globin mRNA, and the protein function encoded by hMDR1 (human multidrug resistance-1) mRNA, while DeltaG(o) (37, hp), a free-energy change for hairpin formations of the antisense ODNs significantly affected the arrest efficiency of the DHFR (dihydrofolate reductase) mRNA transcription, the expression of the proalpha1(I) chain of human, and the hybridization extent for HIV-1 alpha-1. For ras RNA (Ha-ras mRNA), DeltaG(o) (37, sc), a free energy change for the conformational change of the mRNA required for antisense ODN binding showed the best correlation with the equilibrium constants for the hybridization with their target RNA. On the other hand, the antisense effects ifor the HSV-1 IE5 (herpes simplex virus type 1 immediate early pre-mRNA5) showed less of a relationship to the hybridization stability of the antisense ODNs with the target pre-mRNA, because the antisense ODNs targeting the pre-mRNA must collapse its secondary structure around the splicing site to cancel out the expected antisense effects. Based on these results, we illustrate a new concept for the design of antisense ODNs based on DeltaG(o) (37, hyb), DeltaG(o) (37, hp), and DeltaG(o) (37, sc).
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PMID:A new concept for the design of antisense oligonucleotides based on nucleic acid thermostability. 1267 72

Molecular dynamics simulations of the temperature-induced unfolding reaction of native dimeric dihydrofolate reductase from the hyperthermophile Thermatoga maritima (TmDHFR) and the experimentally inaccessible TmDHFR monomer were carried out at 400 K, 450 K and 500 K. The results revealed that the unfolding of TmDHFR subunits followed a similar path to that of the monomeric DHFR from the mesophile E. coli (EcDHFR). An initial collapse of the adenosine-binding domain (ABD) was followed by the loss of the N-terminal and loop domains (NDLD). Interestingly, the elements of the secondary structure of the isolated TmDHFR monomer were maintained for significantly longer periods of time for the hyperthermophilic enzyme, suggesting that subunit stability contributes to the enhanced resistance of TmDHFR to temperature-induced unfolding. The interactions between the subunits of the TmDHFR dimer led to a stabilisation of the NDLD. The hydrogen bonds between residues 140-143 in betaG of one subunit and residues 125-127 in betaF of the other subunit were retained for significant parts of the simulations at all temperatures. These intermolecular hydrogen bonds were lost after the unfolding of the individual subunits. The high stability of the dimer mediated by strong intersubunit contacts together with an intrinsically enhanced stability of the subunits compared to EcDHFR provides a molecular rational for the higher stability of the thermophilic enzyme. The computed unfolding pathways suggest that the partly folded dimer may be a genuine folding intermediate.
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PMID:Molecular dynamics simulation of thermal unfolding of Thermatoga maritima DHFR. 1726 82