Abstract
Bacillithiol is a low molecular weight thiol found in Firmicutes that is analogous to glutathione, which is absent in these bacteria. Bacillithiol transferases catalyze the transfer of bacillithiol to various substrates. The S-transferase-like (STL) superfamily contains over 30,000 putative members, including bacillithiol transferases. Proteins in this family are extremely divergent and are related by structural rather than sequence similarity, leaving it unclear if all share the same biochemical activity. Bacillus subtilis encodes eight predicted STL superfamily members, only one of which has been shown to be a bacillithiol transferase. Here we find that the seven remaining proteins show varying levels of metal dependent bacillithiol transferase activity. We have renamed the eight enzymes BstA-H. Mass spectrometry and gene expression studies revealed that all of the enzymes are produced to varying levels during growth and sporulation, with BstB and BstE being the most abundant and BstF and BstH being the least abundant. Interestingly, several bacillithiol transferases are induced in the mother cell during sporulation. A strain lacking all eight bacillithiol transferases showed normal growth in the presence of stressors that adversely affect growth of bacillithiol-deficient strains, such as paraquat and CdCl2. Thus, the STL bacillithiol transferases represent a new group of proteins that play currently unknown, but potentially significant roles in bacillithiol-dependent reactions. We conclude that these enzymes are highly divergent, perhaps to cope with an equally diverse array of endogenous or exogenous toxic metabolites and oxidants.
Highlights
Low molecular weight thiols (LMWTs) are small, non-protein organosulfur molecules that play many roles in the cell
Using the previously described B. subtils YfiT S-transferase[22] as a query for structural similarity using the Superfamily website[24], we showed that whereas S. aureus encodes only one STL family member, the bacillithiol transferase BstA, Bacillus subtilis encodes a total of eight STL family members, seven of which are putative bacillithiol transferases
To understand the evolutionary relationships between these proteins, we first performed alignments with the primary amino acid sequences of the B. subtilis enzymes (Figure A in S1 File). This analysis showed that B. subtilis BstA and the remaining seven putative B. subtilis bacillithiol transferases share very low sequence identity: BstA showed between 9–23% identity to the remaining transferases, and the most closely related pair (YisT and DinB) showed just 37% sequence identity
Summary
Low molecular weight thiols (LMWTs) are small, non-protein organosulfur molecules that play many roles in the cell They serve as cytoplasmic redox buffers, protect cysteine residues from overoxidation, and they can detoxify harmful molecules that are either produced intracellularly and/or encountered from the extracellular environment[1,2]. Identification of STL enzymes encoded by B. subtilis biotechnology startup company for which she serves as co-founder, consultant, and board member The relationship between this company and the research supported by this grant is being managed by the UCSD Independent Review Committee on Conflict of Interest to ensure that the research is conducted according to federal and campus guidelines. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials
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