Medicine and Health Sciences


Paul D. Cook


Bacillithiol is a low molecular weight thiol that reduces oxidative stress and regulates thiol homeostasis in some Gram-positive bacteria, including the pathogenic Bacillus anthracis and Staphylococcus aureus. It has recently been determined that bacillithiol plays a key role in resistance to the FDA-approved antibiotic fosfomycin. The biosynthesis of BSH is believed to occur via a three step pathway utilizing the enzymes BshA, BshB, and BshC. BshA replaces UDP with malate on UDP-N-acetylglucosamine. BshB acts as a deacetylase to produce glucosaminyl-malate, and BshC is proposed to add cysteine to glucosaminyl-malate to produce bacillithiol. The first solved structure of BshC from Bacillus subtilus contains three key domains of interest. The first is the active site which putatively adds a cysteine to glucosaminyl-malate. The coiled-coil portion forms a tail-like projection that allows dimerization and is a highly conserved region. The third domain of interest contains an ADP molecule. The function of this domain is highly uncertain, and the amino acid residues are not highly conserved among BshC from various species. PHYRE2 was be used to generate a hypothetical model of BshC from S. aureus. The BshC gene was isolated from S. aureus genomic DNA. After expressing and isolating the protein, protein crystals will be analyzed via x-ray crystallography to gain insight into the different domains of interest. Functional analysis of BshC will also be pursued to clue into the mechanism dictating its activity. Understanding how BshC functions will allow specific inhibitors to be designed to stop bacillithiol biosynthesis and re-establish fosfomycin as an effective antibiotic once again.