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Prostaglandin H synthase-1: evaluation of C-terminus function
Y Ren1, D S Loose-Mitchell, R J Kulmacz
1Department of Internal Medicine, University of Texas Health Science Center at Houston 77030.
Archives of Biochemistry and Biophysics
|February 1, 1995
Summary
The C-terminal region of prostaglandin H synthase-1 (PGHS-1) is crucial for its catalytic activity but not for its endoplasmic reticulum localization. Mutations affecting this region impact enzyme function.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Prostaglandin H synthase (PGHS) catalyzes a key step in prostaglandin biosynthesis.
- PGHS is localized to the endoplasmic reticulum (ER) membrane.
- C-terminal motifs can mediate ER retention in other proteins.
Purpose of the Study:
- To investigate the role of C-terminal signals in the ER localization and catalytic activity of human PGHS-1.
- To determine if specific C-terminal mutations affect PGHS-1's subcellular distribution and function.
Main Methods:
- Site-directed mutagenesis of human PGHS-1 C-terminus.
- Expression of wild-type and mutant PGHS-1 in transfected COS-1 cells.
- Subcellular localization assessment via differential centrifugation and immunofluorescence microscopy.
- Enzyme activity assays and limited proteolysis.
Main Results:
- PGHS-1 mutations did not alter its distribution between microsomes and other cellular fractions.
- All tested PGHS-1 mutants colocalized with the ER marker protein disulfide isomerase.
- Mutations at the terminal leucine or deletion of the C-terminus abolished cyclooxygenase activity.
- Terminal leucine mutation altered protein folding, correlating with activity loss.
Conclusions:
- The extreme C-terminal region of PGHS-1 is essential for its functional integrity, not its ER targeting.
- Intracellular targeting of PGHS-1 does not rely on the tested C-terminal retention signals.
- C-terminal modifications can disrupt PGHS-1's catalytic activity through altered protein folding.