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Functional analysis of disease-causing mutations in human galactokinase
David J Timson1, Richard J Reece
1School of Biological Sciences, University of Manchester, United Kingdom.
European Journal of Biochemistry
|April 16, 2003
Summary
Galactokinase (GALK1) is crucial for galactose metabolism and preventing cataracts. Researchers studied enzyme function and mutations causing galactosemia, finding some mutations reduce activity, impacting disease understanding.
Area of Science:
- Biochemistry
- Enzymology
- Human Genetics
Background:
- Galactokinase (GALK1) catalyzes the initial ATP-dependent phosphorylation of galactose.
- Deficiency in functional GALK1 is a cause of galactosemia, leading to early-onset cataracts.
Purpose of the Study:
- To characterize the kinetic mechanism of human galactokinase (GALK1).
- To investigate the functional impact of galactosemia-associated mutations on GALK1 activity and stability.
Main Methods:
- Recombinant human GALK1 was expressed and purified from E. coli.
- Enzyme kinetics, product inhibition, and solvent kinetic isotope effects were analyzed.
- Ten galactosemia-linked GALK1 mutations were created and expressed in E. coli for functional assessment.
Main Results:
- Recombinant GALK1 was soluble and active, exhibiting an ordered ternary complex kinetic mechanism with ATP binding first.
- No significant solvent kinetic isotope effect was observed, suggesting proton transfer is not rate-limiting.
- Five of ten mutations resulted in insoluble protein; four remaining mutants showed reduced activity, while one (A198V) retained wild-type properties.
Conclusions:
- The study elucidates GALK1's kinetic mechanism and the structure-function relationships of disease-causing mutations.
- Understanding how specific mutations affect GALK1 function provides insights into the molecular basis of galactosemia and cataract formation.