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One site mutation disrupts dimer formation in human DPP-IV proteins
Chia-Hui Chien1, Li-Hao Huang, Chi-Yuan Chou
1Division of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Taipei 115, Taiwan, Republic of China.
The Journal of Biological Chemistry
|September 28, 2004
Summary
The C-terminal loop of dipeptidyl peptidase-IV (DPP-IV) is crucial for its dimer formation and catalytic activity. Mutations affecting this loop, particularly His750, lead to reduced enzymatic function and altered quaternary structure, impacting diabetes drug development.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Dipeptidyl peptidase-IV (DPP-IV) is a key enzyme in glucose metabolism and a significant drug target for type II diabetes.
- DPP-IV functions as a dimer, with monomeric forms previously thought to be inactive.
Purpose of the Study:
- To investigate the role of the C-terminal loop and specific residues in DPP-IV dimer formation and catalytic activity.
- To characterize the enzymatic properties of monomeric DPP-IV mutants.
Main Methods:
- Quaternary structure determination using chemical cross-linking, gel electrophoresis, size exclusion chromatography, and analytical ultracentrifugation.
- Enzymatic activity assays (kcat determination) for wild-type and mutant DPP-IV enzymes.
- Site-directed mutagenesis (H750A and H750E).
Main Results:
- The C-terminal loop, particularly His750, is essential for DPP-IV dimer stability and optimal catalysis.
- H750A mutation yields a mix of dimer and monomer, with the monomer showing significantly reduced activity (60-fold decrease in kcat).
- H750E mutation results in predominantly monomeric DPP-IV with a substantial loss of catalytic activity (300-fold decrease in kcat).
Conclusions:
- The C-terminal loop is critical for maintaining DPP-IV's dimeric structure and enzymatic function.
- Monomeric DPP-IV exhibits significantly impaired catalytic activity.
- Findings provide insights into DPP-IV structure-function relationships and have implications for designing drugs targeting the dimer interface for diabetes treatment.