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Long-range interactions in the dimer interface of ornithine decarboxylase are important for enzyme function
D P Myers1, L K Jackson, V G Ipe
1Department of Pharmacology, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9041, USA.
Biochemistry
|October 31, 2001
Summary
Ornithine decarboxylase (ODC) is crucial for polyamine synthesis and a drug target for sleeping sickness. Interface mutations primarily affect ODC
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis.
- ODC is a validated drug target for treating African sleeping sickness.
- ODC functions as an obligate homodimer with active sites at the dimer interface.
Purpose of the Study:
- To investigate the energetic contribution of dimer interface residues to subunit association in Trypanosoma brucei ODC.
- To determine how mutations at the ODC dimer interface affect enzyme stability and catalytic efficiency.
Main Methods:
- Alanine scanning mutagenesis was performed on dimer interface residues of Trypanosoma brucei ODC.
- Analytical ultracentrifugation was used to assess the stability of 23 mutant enzymes.
- Catalytic efficiency (kcat/Km) was measured to evaluate the impact of mutations on enzyme function.
Main Results:
- No significant decrease in dimer stability (less than 1 kcal/mol) was observed for any of the 23 mutations.
- Many mutations significantly impacted catalytic efficiency (DeltaDeltaG kcat/Km > 2.5 kcal/mol).
- Mutations affecting activity were located both near the active site and at distant positions (15-20 A), suggesting long-range coupling.
Conclusions:
- The ODC dimer interface is optimized for catalytic function rather than subunit association stability.
- Long-range energetic coupling between interface residues and the active site is essential for ODC function.
- Targeting the ODC dimer interface with small molecules could modulate enzyme activity without disrupting dimerization.
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