Reconstitution of mitochondrial protein transport with purified ornithine carbamoyltransferase precursor expressed in Escherichia coli.
Ornithine carbamoyltransferase (OTC; subunit, 36,000 Da) is initially synthesized as a precursor (pOTC) with a transient NH2-terminal presequence of 32 amino acid residues and imported posttranslationally into the mitochondrial matrix. The rat pOTC was synthesized in Escherichia coli using an expression vector containing a thermoinducible lambda pL promoter. The recombinant pOTC represented 5-10% of the total bacterial protein and was present in the precipitate of the disrupted bacteria. The precipitate was washed and pOTC was extracted with 8 M urea or 0.1% cetyltrimethylammonium bromide. The extracted pOTC was essentially homogeneous, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified pOTC was cleaved to the intermediate-sized product of 37,000 Da by a processing protease partially purified from the matrix fraction of rat liver mitochondria. The purified recombinant pOTC, but not the mature form of OTC synthesized in E. coli and purified, competed with the in vitro-synthesized, radiolabeled pOTC for uptake and processing by the isolated rat liver mitochondria. The radiolabeled and purified recombinant pOTC could be imported into the isolated mitochondria and processed to the mature form in an energy- and rabbit reticulocyte lysate-dependent manner. When the purified pOTC was subjected to sucrose gradient centrifugation, it sedimented as a large aggregate of greater than 60 S in the absence of reticulocyte lysate, whereas it sedimented as a complex of about 5 S in the presence of the lysate. These observations together with our previous results indicate that a protein factor(s) present in the lysate interacts with pOTC and holds it in an import-competent form.
Murakami
K
K
Institute for Medical Genetics, Kumamoto University Medical School, Japan.
Amaya
Y
Y
Takiguchi
M
M
Ebina
Y
Y
Mori
M
M
D000818:Animals; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D008930:Mitochondria, Liver / Q000201:enzymology*; D008970:Molecular Weight; D009954:Ornithine Carbamoyltransferase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism*
D004792:Enzyme Precursors; D011994:Recombinant Proteins; D009954:Ornithine Carbamoyltransferase