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L-aspartase: new tricks from an old enzyme
1Department of Chemistry, University of Akron, Ohio 44325-3601, USA.
Summary
L-aspartate ammonia-lyase (aspartase) is a highly specific enzyme. Recent studies reveal aspartase has unexpected properties, including a regulatory site and enhanced activity or new biological functions upon carboxyl-terminal truncation.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- L-aspartate ammonia-lyase (aspartase) catalyzes L-aspartic acid deamination via a carbanion mechanism.
- Aspartase exhibits extreme substrate specificity, with limited success in identifying alternative substrates.
- Sequence homology links aspartase to fumarases and other lyases, suggesting conserved structural and functional roles.
Purpose of the Study:
- To explore the structure-function relationship of aspartase.
- To investigate recent findings on the enzyme's unexpected properties and catalytic mechanisms.
- To understand the impact of structural modifications on aspartase activity and potential new functions.
Main Methods:
- High-resolution structural analysis of aspartase.
- Mutagenic studies to identify active site residues.
- Kinetic analyses to characterize enzyme behavior under various conditions.
- Carboxyl-terminal truncation experiments to assess functional changes.
Main Results:
- The high-resolution structure reveals a monomer with three domains forming an S-shape, with active sites located in inter-subunit clefts.
- Non-linear kinetics were attributed to a distinct regulatory site, where aspartic acid and a divalent metal ion act as an activator.
- Carboxyl-terminal truncation enhanced catalytic activity and introduced a novel non-enzymatic function: enhancing plasminogen activation.
Conclusions:
- Aspartase, despite being well-characterized, possesses complex regulatory mechanisms and novel functionalities.
- Structural insights and functional studies continue to reveal the multifaceted nature of aspartase.
- Further exploration is warranted to fully elucidate the remaining aspects of this enzyme's biology and potential applications.
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