Metal Ions Stabilize a Dimeric Molten Globule State between the Open and Closed Forms of Malic Enzyme
| Autor: | Hui Chuan Chang, Gu-Gang Chang, Yi Hang Lu, Meng Ying Li, Yu Hou Chen, Chao Hsiung Lin, Liang Yu Chen |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2007 |
| Předmět: |
chemistry.chemical_classification
Conformational change Protein Folding Stereochemistry Protein Conformation Biophysics Malic enzyme food and beverages Proteins Molten globule Phase Transition Protein structure Enzyme Biochemistry chemistry Malate Dehydrogenase Metals Enzyme Stability Protein quaternary structure Protein folding NAD+ kinase |
| Popis: | Malic enzyme is a tetrameric protein with double dimer quaternary structure. In 3-5 M urea, the pigeon cytosolic NADP(+)-dependent malic enzyme unfolded and aggregated into various forms with dimers as the basic unit. Under the same denaturing conditions but in the presence of 4 mM Mn(2+), the enzyme existed exclusively as a molten globule dimer in solution. Similar to pigeon enzyme (Chang, G. G., T. M. Huang, and T. C. Chang. 1988. Biochem. J. 254:123-130), the human mitochondrial NAD(+)-dependent malic enzyme also underwent a reversible tetramer-dimer-monomer quaternary structural change in an acidic pH environment, which resulted in a molten globule state that is also prone to aggregate. The aggregation of pigeon enzyme was attributable to Trp-572 side chain. Mutation of Trp-572 to Phe, His, Ile, Ser, or Ala abolished the protective effect of the metal ions. The cytosolic malic enzyme was completely digested within 2 h by trypsin. In the presence of Mn(2+), a specific cutting site in the Lys-352-Gly-Arg-354 region was able to generate a unique polypeptide with M(r) of 37 kDa, and this polypeptide was resistant to further digestion. These results indicate that, during the catalytic process of malic enzyme, binding metal ion induces a conformational change within the enzyme from the open form to an intermediate form, which upon binding of L-malate, transforms further into a catalytically competent closed form. |
| Databáze: | OpenAIRE |
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