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Enzyme mechanisms for sterol C-methylations.
1Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA. wdavid.nes@ttu.edu
Phytochemistry
|August 30, 2003
Summary
Sterol methyl transferases (SMTs) catalyze complex C-methylation reactions. Recent research clarifies their ancient origins, enzymatic mechanisms, and the steric-electric plug model, revealing insights into sterol pathway evolution and regulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Sterol methyl transferases (SMTs) are enzymes with complex mechanisms for C-methylation.
- Over 50 years of research has focused on understanding how SMTs transform olefins into diverse methylated sterols.
Purpose of the Study:
- To provide new insights into the enzymatic mechanisms of sterol C-methylation.
- To establish a basis for understanding the regulation and evolution of the sterol pathway.
- To review the mechanism of C-methylation and how point mutations can alter sterol structure.
Main Methods:
- Enzymological studies
- Analysis of fossil records
- Functional analyses
- Gene cloning
Main Results:
- SMTs likely originated early in Earth's history.
- SMTs align pi-electrons of the Delta(24)-double bond with AdoMet's S-methyl group.
- The steric-electric plug model explains substrate binding, stereospecificity, and product diversity.
- Point mutations can alter SMT function and sterol structure.
Conclusions:
- Recent studies have significantly advanced our understanding of SMT mechanisms, regulation, and evolution.
- SMTs play a crucial role in phytosterol homeostasis and are subject to feedback regulation.
- The steric-electric plug model offers a unified framework for SMT action.