Recognition of partially-folded mitochondrial malate dehydrogenase by GroEL. Steady and time-dependent emission anisotropy measurements. |
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Authors: | J E Churchich |
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Institution: | Department of Biochemistry, University of Tennessee, Knoxville 37996-0840, USA. |
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Abstract: | The binding of partially-folded mitochondrial malate dehydrogenase (mMDH) to GroEL was assessed by steady and nanosecond emission spectroscopy. Partially-folded intermediates of mMDH show significant residual secondary structure when examined by CD spectroscopy in the far UV. They bind the extrinsic fluorescent probe ANS and the protein-ANS complexes display a rotational correlation time of 19 ns. Similar rotational correlation time (phi = 18.6 ns) was determined for partially-folded species tagged with anthraniloyl. GroEL recognizes partially-folded species with a K(D) approximately 60 nM. The rotational correlation time of the complex, i.e., GroEL-mMDH-ANT, approaches a value of 280 ns in the absence of ATP. Reactivation of mMDH-ANT by addition of GroEL and ATP brings about a significant decrease in the observed rotational correlation time. The results indicate that partially-folded malate dehydrogenase is rigidly trapped by GroEL in the absence of ATP, whereas addition of ATP facilitates reactivation and release of folded conformations endowed with catalytic activity. |
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Keywords: | fluorescence spectroscopy GroEL partially-folded mitochondrial malate dehydrogenase protein-protein interaction time-dependent emission anisotropy |
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