Stability and release requirements of the complexes of GroEL with two homologous mammalian aminotransferases.
The mitochondrial (mAAT) and cytosolic (cAAT) homologous isozymes of aspartate aminotransferase are two relatively large proteins that in their nonnative states interact very differently with GroEL. MgATP alone can increase the rate of GroEL-assisted reactivation of cAAT, yet the presence of GroES is mandatory for mAAT. Addition of an excess of a denatured substrate accelerates reactivation of cAAT in the presence of GroEL, but has no effect on mAAT. These competition studies suggest that the more stringent substrate mAAT forms a thermodynamically stable complex with GroEL, while rebinding affects the slow reactivation kinetics of cAAT with GroEL alone. However, the competitor appears to accelerate the release of cAAT from GroEL, most likely by displacing bound cAAT from the GroEL cavity. Moreover, cAAT, but not mAAT, shows a time-dependent increase in protease resistance while bound to GroEL at low temperature. These results suggest that folding and release of cAAT from GroEL in the absence of cofactors may occur stepwise with certain interactions being broken and reformed until the protein escapes binding. The distinct behavior of these two isozymes most likely results from differences in the structure of the nonnative states that bind to GroEL.
Scherrer
S
S
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, 64110-2499, USA.
Iriarte
A
A
Martinez-Carrion
M
M
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001219:Aspartate Aminotransferases / Q000737:chemistry* / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D018835:Chaperonin 10 / Q000494:pharmacology; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D004355:Drug Stability; D006801:Humans; D007700:Kinetics; D008322:Mammals; D008928:Mitochondria / Q000201:enzymology; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D020673:Protein Renaturation / Q000187:drug effects; D017386:Sequence Homology, Amino Acid
D018835:Chaperonin 10; D018834:Chaperonin 60; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate; D001219:Aspartate Aminotransferases