Cross-functionalities of Bacillus deacetylases involved in bacillithiol biosynthesis and bacillithiol-S-conjugate detoxification pathways

摘要

pBshB, a key enzyme in bacillithiol biosynthesis, hydrolyses the acetyl group from iN/i-acetylglucosamine malate to generate glucosamine malate. In iBacillus anthracis/i, BA1557 has been identified as the iN/i-acetylglucosamine malate deacetylase (BshB); however, a high content of bacillithiol (~70%) was still observed in the iB. anthracis/i ?iBA1557/i strain. Genomic analysis led to the proposal that another deacetylase could exhibit cross-functionality in bacillithiol biosynthesis. In the present study, BA1557, its paralogue BA3888 and orthologous iBacillus cereus/i enzymes BC1534 and BC3461 have been characterized for their deacetylase activity towards iN/i-acetylglucosamine malate, thus providing biochemical evidence for this proposal. In addition, the involvement of deacetylase enzymes is also expected in bacillithiol-detoxifying pathways through formation of S-mercapturic adducts. The kinetic analysis of bacillithiol-S-bimane conjugate favours the involvement of BA3888 as the iB. anthracis/i bacillithiol-S-conjugate amidase (Bca). The high degree of specificity of this group of enzymes for its physiological substrate, along with their similar pH–activity profile and Znsup2+/sup-dependent catalytic acid–base reaction provides further evidence for their cross-functionalities./p