Optimized production and purification of Bacillus anthracis lethal factor

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Bacillus anthracis lethal factor (LF) is a critical virulence factor, a 90-kDa zinc metalloprotease.
• Previous purification methods from Escherichia coli and Bacillus anthracis yielded insufficient protein purity and quantity for structural determination.
• Determining the crystal structure of LF is essential for understanding its mechanism and developing targeted therapeutics or vaccines.

Purpose of the Study:

• To develop an efficient expression and purification system for high-yield, high-purity Bacillus anthracis lethal factor (LF).
• To produce both wild-type and inactive (LF-E687C) LF proteins suitable for crystal structure determination.
• To explore the potential application of purified LF in the development of anthrax vaccines.

Main Methods:

• Genes for wild-type and mutated LF were cloned into an E. coli-Bacillus shuttle vector, utilizing the protective antigen (PA) signal peptide for secretion.
• Expression was driven by the PA promoter, leading to the secretion of 90-kDa LF proteins after signal peptide cleavage.
• Proteins were purified using a three-step chromatography process: Phenyl-Sepharose, Q-Sepharose, and hydroxyapatite.

Main Results:

• The novel expression system achieved significantly higher yields (20-30 mg/L) compared to previous methods (1-5 mg/L).
• Purified wild-type and mutated LF proteins exceeded 95% purity.
• The highly pure LF proteins have been successfully crystallized, enabling ongoing crystal structure determination efforts.

Conclusions:

• This study presents a robust and efficient method for producing high-purity Bacillus anthracis lethal factor (LF).
• The improved yield and purity facilitate structural studies, crucial for understanding LF's function.
• The purified LF holds promise for future development of effective anthrax vaccines.