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The structure and action of chitinases
1Department of Chemistry and Biochemistry, University of Texas, Austin 78712, USA.
EXS
|July 25, 2000
Summary
Chitinases are enzymes that break down chitin, a key component of cell walls. Family 18 chitinases use a retaining mechanism, while Family 19 chitinases, structurally distinct and related to lysozymes, use an inverting mechanism.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Chitin, second only to cellulose in biomass, is a crucial polysaccharide in cell walls.
- Multiple enzyme families have evolved to hydrolyze chitin, exhibiting distinct structures and mechanisms.
- Glycohydrolase Family 18 chitinases possess an alpha/beta barrel structure and act via a retaining mechanism.
Purpose of the Study:
- To compare and contrast the structural and mechanistic properties of different chitinase enzyme families.
- To investigate the evolutionary relationships between chitinases and related enzymes like lysozymes.
Main Methods:
- Structural analysis of Family 19 chitinases.
- Comparison of Family 19 chitinases with Family 18 chitinases and lysozymes.
- Amino acid sequence analysis to infer evolutionary relationships.
Main Results:
- Family 19 chitinases, primarily found in plants and bacteria, have a bilobal, high alpha-helical structure.
- Family 19 chitinases operate through an inverting mechanism, distinct from the retaining mechanism of Family 18 chitinases.
- Structural similarities between Family 19 chitinases, Family 46 chitosanases, and certain lysozymes suggest a common glycohydrolase ancestor.
Conclusions:
- Chitinase evolution involves distinct structural and mechanistic adaptations within different enzyme families.
- Family 19 chitinases represent a separate evolutionary lineage from Family 18 chitinases, despite both acting on chitin.
- The structural data supports an ancient common ancestor for various glycohydrolases, predating prokaryotic/eukaryotic divergence.