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Conformational changes in ornithine decarboxylase enable recognition by antizyme
1Department of Biological Sciences, Northern Illinois University, DeKalb 60115.
Abstract:
Rapid, polyamine-induced degradation of mammalian ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) (ODC) is though to be controlled by the availability of a small, ODC-binding protein termed antizyme. In this study we have investigated the ability of antizyme to bind ODC protein in various altered physiological states. In particular, cold, NaCl, spermidine and deprivation of coenzyme and substrate enhance enzyme-antizyme complex formation and are all found to promote ODC homodimer dissociation. Conversely, conditions that maintain the active ODC homodimer state prevent antizyme binding and inactivation of ODC. Further, covalent modification of ODC near its active site by difluoromethylornithine or phosphate also increases its sensitivity to antizyme. These results suggest that the initial signal in ODC degradation may actually be a subtle conformational change in the enzyme that enables antizyme to bind to the enzyme and may subsequently facilitate its degradation.
Insights
Polyamines regulate ornithine decarboxylase (ODC) degradation via antizyme. ODC conformational changes, influenced by cellular conditions, dictate antizyme binding and subsequent enzyme inactivation.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Ornithine decarboxylase (ODC) is a key enzyme in polyamine synthesis.
- ODC degradation is rapid and polyamine-induced, suggesting regulatory control.
- Antizyme is a known ODC-binding protein implicated in ODC regulation.
Purpose of the Study:
- To investigate the binding of antizyme to ODC under various physiological conditions.
- To understand how cellular states affect the ODC-antizyme interaction and ODC stability.
- To elucidate the initial molecular events triggering ODC degradation.
Main Methods:
- Studying ODC-antizyme complex formation in vitro.
- Analyzing ODC protein in altered physiological states (cold, NaCl, spermidine, coenzyme/substrate deprivation).
- Assessing the impact of ODC covalent modifications (difluoromethylornithine, phosphate) on antizyme sensitivity.
Main Results:
- Cold, NaCl, spermidine, and coenzyme/substrate deprivation enhance ODC-antizyme complex formation.
- These conditions also promote ODC homodimer dissociation, preventing antizyme binding.
- Covalent modification of ODC near the active site increases its sensitivity to antizyme.
Conclusions:
- ODC degradation is initiated by subtle conformational changes in the enzyme.
- These conformational changes facilitate antizyme binding.
- Antizyme binding subsequently leads to ODC inactivation and degradation.