Bacillithiol
Encyclopedia
Bacillithiol is a thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

 compound found in Bacillus
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...

species. Chemically, it is a glycoside formed between L-cysteinyl-D-glucosamine and malic acid
Malic acid
Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms , though only the L-isomer exists...

. It was isolated and identified (as its bacillithiol-S-bimane
Bimane
Bimane is a heterocyclic chemical compound. Bimane forms the core of a class of fluorescent dyes known as bimane dyes....

 derivative) in 2009 from Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

and Deinococcus radiodurans
Deinococcus radiodurans
Deinococcus radiodurans is an extremophilic bacterium, one of the most radioresistant organisms known. It can survive cold, dehydration, vacuum, and acid, and is therefore known as a polyextremophile and has been listed as the world's toughest bacterium in The Guinness Book Of World Records.-Name...

, although it was first detected in 2007, as an unidentified thiol in Bacillus anthracis
Bacillus anthracis
Bacillus anthracis is the pathogen of the Anthrax acute disease. It is a Gram-positive, spore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm. It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.It is one of few bacteria known to...

. The naturally occurring free thiol form of bacillithiol has since been synthesised and characterised along with its biosynthetic precursors and its symmetrical disulfide. Bacillithiol appears to participate in the sensing of peroxide
Peroxide
A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen peroxide...

s by Bacillus, but may also substitute for glutathione
Glutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...

, which is the most common intracellular thiol in other organisms. Some of genes involved in the biosynthesis of bacillithiol were identified and characterized in 2010. Bacteria engineered to be deficient in bacillithiol demonstrated increased sensitivity to various electrophilic xenobiotic
Xenobiotic
A xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it. It can also cover substances which are present in much higher concentrations than are usual...

 compounds, including the antibiotic fosfomycin
Fosfomycin
Fosfomycin is a broad-spectrum antibiotic produced by certain Streptomyces species.-Uses:...

, suggesting that in these organisms the mechanism of fosfomycin resistance relies on the presence of bacillithiol. Kinetic studies have also established that bacillithiol is a preferred thiol substrate for FosB compared to cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

.
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