Related Experiment Videos
Escherichia coli cyclopropane fatty acid synthase
Fabienne Courtois1, Christine Guérard, Xavier Thomas
1Laboratoire de Chimie Organique Biologique, UMR7613 CNRS, Université Pierre et Marie Curie, Paris, France.
European Journal of Biochemistry
|December 21, 2004
Summary
Escherichia coli fatty acid cyclopropane synthase (CFAS) was purified and characterized. Conserved cysteine residues are not essential for CFAS catalysis, suggesting a carbocation mechanism.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Escherichia coli fatty acid cyclopropane synthase (CFAS) is crucial for bacterial membrane lipid biosynthesis.
- Understanding its catalytic mechanism is key to developing novel antimicrobial strategies.
Purpose of the Study:
- To overproduce, purify, and characterize recombinant E. coli CFAS.
- To investigate the role of conserved cysteine residues in CFAS catalysis and mechanism.
Main Methods:
- Overproduction and purification of His6-tagged E. coli CFAS.
- Enzyme kinetics assays (Km, specific activity).
- Site-directed mutagenesis of conserved cysteine residues (C139S, C176S, C354S).
- Enzyme inactivation studies using 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB).
Main Results:
- Recombinant CFAS exhibited activity comparable to the native enzyme.
- The enzyme does not require organic or metal cofactors and does not support proton exchange, ruling out the ylide mechanism.
- DTNB inactivation identified a single essential cysteine residue, which is not among the conserved residues.
- Mutagenesis of conserved cysteines showed they are not essential for catalysis, with C176S exhibiting enhanced activity.
Conclusions:
- Conserved cysteine residues are not essential for E. coli CFAS catalysis.
- The essential cysteine residue involved in DTNB inactivation is likely not involved in the catalytic mechanism.
- E. coli CFAS likely operates via a carbocation mechanism, with the catalytic base and nucleophile yet to be identified.