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Switching desaturase enzyme specificity by alternate subcellular targeting
Ingo Heilmann1, Mark S Pidkowich, Thomas Girke
1Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA.
Summary
Enzyme regiospecificity can be altered by cellular location, not just protein sequence. Targeting enzymes to different compartments, like the plastid, switches their substrate preference, influencing plant lipid metabolism.
Area of Science:
- Biochemistry
- Molecular Biology
- Plant Science
Background:
- Enzyme functionality typically evolves through mutations in catalytic sites.
- Emerging evidence suggests metabolic context influences enzyme activity and specificity.
- Subcellular localization can impact enzyme substrate specificity and regiospecificity.
Purpose of the Study:
- To investigate the role of subcellular localization in determining desaturase regiospecificity.
- To explore how metabolic context, specifically lipid environment, affects enzyme activity.
- To understand the mechanism behind FAD5's Delta7 regiospecificity.
Main Methods:
- Retargeting of Arabidopsis desaturases (FAD5, ADS1, ADS2) to different cellular compartments (plastid, cytoplasm).
- Expression of desaturases in yeast with and without cucumber monogalactosyldiacylglycerol (MGDG) synthase.
- Analysis of desaturated fatty acid products and their lipid localization.
Main Results:
- Retargeting FAD5 to the cytoplasm shifted regiospecificity from Delta7 to Delta9.
- Retargeting ADS1 and ADS2 to the plastid shifted regiospecificity from Delta9 to Delta7.
- Coexpression with MGDG synthase in yeast conferred Delta7 desaturation, with products accumulating on MGDG.
Conclusions:
- Lipid headgroup, specifically MGDG, acts as a molecular switch for desaturase regiospecificity.
- FAD5's Delta7 specificity is primarily due to its plastidial targeting, not sequence differences.
- Alternative subcellular targeting is a widespread mechanism for generating metabolic diversity in plants.