DNA binding by dihydrofolate reductase from Lactobacillus casei.

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Dihydrofolate reductase (DHFR) is a crucial enzyme in folate metabolism.
• Understanding protein-DNA interactions is fundamental to molecular biology.
• Lactobacillus casei DHFR's structure is well-characterized.

Purpose of the Study:

• To investigate the direct DNA-binding affinity of pure Lactobacillus casei dihydrofolate reductase.
• To determine if DNA binding is influenced by coenzymes or inhibitors.
• To explore potential specific DNA-protein interactions involving the DHFR gene region.

Main Methods:

• Protein-dependent nitrocellulose filter retention assays were employed.
• Binding affinities were tested using linear and supercoiled double-stranded DNA.
• Comparative DNA binding was assessed using plasmid DNA with and without the L. casei DHFR gene insert.

Main Results:

• Lactobacillus casei dihydrofolate reductase exhibits a clear affinity for double-stranded DNA.
• DNA binding is unaffected by common coenzymes and inhibitors, suggesting a distinct DNA-binding domain.
• A specific interaction may occur with DNA containing the L. casei DHFR gene, requiring lower protein concentrations for retention.

Conclusions:

• Lactobacillus casei dihydrofolate reductase directly binds DNA independently of its catalytic function.
• The enzyme possesses a DNA-binding region distinct from its active site.
• The findings open avenues for studying DHFR-DNA interactions, leveraging existing structural and NMR data.