Precursor of mitochondrial aspartate aminotransferase synthesized in Escherichia coli is complexed with heat-shock protein DnaK.
On expression of the cDNA encoding the precursor of chicken mitochondrial aspartate aminotransferase (pmAspAT) in Escherichia coli, the bulk of pmAspAT was found to be associated with the 70-kDa heat-shock protein DnaK which is closely related to mitochondrial 70-kDa heat-shock protein (HSP70). Purification protocols for the DnaK/pmAspAT complex and its individual components were elaborated. The complex dissociated on treatment with MgATP or at pH 5.5. Like the mature enzyme, pmAspAT is a dimer (2 x 47 kDa) and exhibits about a third of its enzyme activity. In the DnaK/pmAspAT complex, one DnaK molecule is bound to each subunit of pmAspAT; this tetramer may further aggregate to an octamer. The complex is catalytically almost as active as free pmAspAT. It could be reconstituted from isolated DnaK and pmAspAT. No complex was formed with mAspAT. Apparently, DnaK binds to the solvent-exposed presequence of folded pmAspAT without significantly changing the structure and functional properties of its mature moiety.
Schmid
D
D
Biochemisches Institut, Universität Zürich, Switzerland.
Jaussi
R
R
Christen
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001219:Aspartate Aminotransferases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D002645:Chickens; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D046911:Macromolecular Substances; D008928:Mitochondria / Q000201:enzymology; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012995:Solubility
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D011498:Protein Precursors; D011994:Recombinant Proteins; D001219:Aspartate Aminotransferases; C063842:dnaK protein, E coli