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Phosphorylation of a UDP-glucuronosyltransferase regulates substrate specificity
Nikhil K Basu1, Martina Kovarova, Amanda Garza
1Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Building 10, Room 9S-241, Bethesda, MD 20892-1830, USA.
Summary
Protein kinase C (PKC) phosphorylates UDP-glucuronosyltransferase (UGT) enzymes, altering their substrate specificity for detoxification. This phosphorylation mechanism, involving specific serine/threonine sites, helps cells adapt to environmental toxins.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- UDP-glucuronosyltransferase (UGT) isozymes detoxify xenobiotics via glucuronidation.
- The mechanisms governing endoplasmic reticulum-bound UGTs' substrate specificity remain largely unknown.
Purpose of the Study:
- To elucidate the enzymatic mechanism and regulatory pathways of UGT isozymes.
- To investigate the role of protein phosphorylation in UGT function and substrate specificity.
Main Methods:
- Inhibition assays with specific peptides and chemicals.
- Co-immunoprecipitation, immunofluorescence, and cross-linking studies.
- Site-directed mutagenesis of UGT isozymes and activity assays.
Main Results:
- UGT1A7 and UGT1A10 were found to be phosphorylated, with PKCepsilon involvement confirmed.
- Specific phosphorylation sites (T73, T202, S432) were identified as critical for UGT activity and substrate specificity.
- PKCepsilon overexpression enhanced UGT1A7 activity, while inhibition studies revealed PKC-mediated regulation of 17beta-estradiol catalysis.
Conclusions:
- A novel mechanism of UGT regulation via PKC-mediated phosphorylation is described.
- Phosphorylation at specific serine/threonine residues modulates UGT substrate specificity in response to chemical exposures.
- This regulatory pathway may confer a survival advantage by enhancing detoxification capabilities.