Comparative study on conformational stability and subunit interactions of two bacterial asparaginases

Area of Science:

• Biochemistry
• Enzymology
• Protein chemistry

Background:

• L-asparaginase enzymes are crucial in cancer therapy, particularly for acute lymphoblastic leukemia.
• Understanding the structural dynamics of L-asparaginase is vital for optimizing its therapeutic efficacy and stability.

Purpose of the Study:

• To investigate the denaturation and reconstitution processes of Erwinia carotovora and Escherichia coli L-asparaginases.
• To determine the optimal conditions for refolding denatured L-asparaginase subunits into enzymatically active forms.
• To analyze the kinetics of dissociation and conformational changes during these processes.

Main Methods:

• Optical rotatory dispersion (ORD)
• Circular dichroism (CD) spectroscopy
• Analytical ultracentrifugation
• Enzyme activity assays

Main Results:

• Denaturation in urea led to the dissociation of native L-asparaginase (140,000 Da) into subunits (35,000 Da).
• Refolding in alkaline conditions (pH 10.5) yielded unstable monomers/dimers, while refolding between pH 5.0-7.5 successfully reformed the active tetramer in up to 80% yield.
• Sodium dodecyl sulfate induced conformational changes in both native and refolded subunits.

Conclusions:

• The refolding efficiency of L-asparaginase is highly dependent on pH, with neutral to slightly acidic conditions favoring the formation of the active tetramer.
• Dissociation of subunits is a rate-limiting step in the denaturation/reconstitution process.
• These findings have implications for the stability and therapeutic application of L-asparaginase.