The superfamily of glutathione S-transferases has been the subject of extensive study but Actinobacteria produce mycothiol (MSH) in place of glutathione and no mycothiol S-transferase (MST) has been identified. Using mycothiol and monochlorobimane as substrates a MST activity was detected in extracts of Mycobacterium smegmatis and purified sufficiently to allow identification of MSMEG_0887, a member the DUF664 family of the DinB superfamily, as the MST. The identity of the M. smegmatis and homologous Mycobacterium tuberculosis (Rv0443) enzymes was confirmed by cloning and the expressed proteins were found to be active with MSH but not bacillithiol (BSH) or glutathione (GSH). Bacillus subtilis YfiT is another member of the DinB superfamily but this bacterium produces BSH. The YfiT protein was shown to have S-transferase activity with monochlorobimane when assayed with BSH but not with MSH or GSH. Enterococcus faecalis EF_3021 shares some homology with MSMEG_0887 but this organism produces GSH but not MSH or BSH. Cloned and expressed EF_0321 was active with monochlorobimane and GSH but not with MSH or BSH. MDMPI_2 is another member of the DinB superfamily and has been previously shown to have mycothiol-dependent maleylpyruvate isomerase activity. Three of the eight families of the DinB superfamily include proteins shown to catalyze thiol-dependent metabolic or detoxification activities. Since more than two-thirds of the sequences assigned to the DinB superfamily are members of these families it seems likely that such activity is dominant in the DinB superfamily.

The full monty: The recently discovered thiol cofactor bacillithiol (BSH), its biosynthetic precursors, and its symmetrical disulfide are prepared in two ways. The fosfomycin resistance protein (FosB) is shown to be a BSH‐utilizing enzyme. It displays bacillithiol‐S‐transferase activity with a strong preference for BSH over L‐cysteine as its thiol substrate.

Das volle Programm: Der kürzlich entdeckte Thiol‐Cofaktor Bacillithiol (BSH), seine Biosynthesevorstufe und sein symmetrisches Disulfid wurden auf zwei Arten hergestellt. Das Fosfomycinresistenzprotein (FosB) zeigt BSH‐S‐Transferaseaktivität mit einer starken Bevorzugung von BSH gegenüber L‐Cystein als Thiolsubstrat.