Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mitochondrial aspartate aminotransferase is inactivated irreversibly on heating. The inactivated protein aggregates, but aggregation is prevented by the presence of the chaperonin 60 from Escherichia coli (GroEL). The chaperonin increases the rate of thermal inactivation in the temperature range 55-65 degrees C but not at lower temperatures. It has previously been shown [Twomey and Doonan (1997) Biochim. Biophys. Acta 1342, 37-44] that the enzyme switches to a modified, but catalytically active, conformation at approx. 55-60 degrees C and the present results show that this conformation is recognized by and binds to GroEL. The thermally inactivated protein can be released from GroEL in an active form by the addition of chaperonin 10 from E. coli (GroES)/ATP, showing that inactivation is not the result of irreversible chemical changes. These results suggest that the irreversibility of thermal inactivation is due to the formation of an altered conformation with a high kinetic barrier to refolding rather than to any covalent changes. In the absence of chaperonin the unfolded molecules aggregate but this is a consequence, rather than the cause, of irreversible inactivation.
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PMID:Thermal inactivation and chaperonin-mediated renaturation of mitochondrial aspartate aminotransferase. 969 23

The partially homologous mitochondrial (mAAT) and cytosolic (cAAT) aspartate aminotransferase have nearly identical three-dimensional structures but differ in their folding rates in cell-free extracts and in their affinity for binding to molecular chaperones. In its native state, each isozyme is protease-resistant. Using limited proteolysis as an index of their conformational states, we have characterized these proteins (a) during the early stages of spontaneous refolding; (b) as species trapped in stable complexes with the chaperonin GroEL; or (c) as newly translated polypeptides in cell-free extracts. Treatment of the refolding proteins with trypsin generates reproducible patterns of large proteolytic fragments that are consistent with the formation of defined folding domains soon after initiating refolding. Binding to GroEL affords considerable protection to both isozymes against proteolysis. The tryptic fragments are similar in size for both isozymes, suggesting a common distribution of compact and flexible regions in their folding intermediates. cAAT synthesized in cell-free extracts becomes protease-resistant almost instantaneously, whereas trypsin digestion of the mAAT translation product produces a pattern of fragments qualitatively akin to that observed with the protein refolding in buffer. Analysis of the large tryptic peptides obtained with the GroEL-bound proteins reveals that the cleavage sites are located in analogous regions of the N-terminal portion of each isozyme. These results suggest that (a) binding to GroEL does not cause unfolding of AAT, at least to an extent detectable by proteolysis; (b) the compact folding domains identified in AAT bound to GroEL (or in mAAT fresh translation product) are already present at the early stages of refolding of the proteins in buffer alone; and (c) the two isozymes seem to bind in a similar fashion to GroEL, with the more compact C-terminal portion completely protected and the more flexible N-terminal first 100 residues still partially accessible to proteolysis.
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PMID:Conformation of aspartate aminotransferase isozymes folding under different conditions probed by limited proteolysis. 972 49