Altered β-Lactamase Selection Approach for Site-Directed Mutagenesis

Area of Science:

• Molecular Biology
• Enzymology
• Microbiology

Background:

• Site-directed mutagenesis is crucial for protein engineering.
• Beta-lactamase enzymes hydrolyze beta-lactam antibiotics like ampicillin.
• Mutations can alter beta-lactamase substrate specificity and activity.

Purpose of the Study:

• To present a site-directed mutagenesis protocol utilizing altered beta-lactamase selection.
• To demonstrate the selection of mutated plasmids based on altered enzyme properties.

Main Methods:

• Employing a beta-lactamase triple mutant (G238S:E240:R241G) in E. coli.
• Utilizing altered substrate specificity for cephalosporins (cefotaxime, ceftriaxone) as a selection marker.
• Selecting for plasmids conferring resistance to cephalosporins.

Main Results:

• The beta-lactamase triple mutant exhibits increased hydrolytic activity against cephalosporins.
• E. coli cells with the mutant enzyme show enhanced resistance to cefotaxime and ceftriaxone.
• This differential resistance allows for the selection of mutated plasmids.

Conclusions:

• Altered beta-lactamase selection is an effective method for site-directed mutagenesis.
• The G238S:E240:R241G beta-lactamase mutant serves as a valuable tool for plasmid selection.
• This protocol facilitates the generation and identification of specific gene mutations.