Tat–Dependent Translocation of an F420–Binding Protein of Mycobacterium tuberculosis

F 420 is a unique cofactor present in a restricted range of microorganisms, including mycobacteria. It has been proposed that F 420 has an important role in the oxidoreductive reactions of Mycobacterium tuberculosis , possibly associated with anaerobic survival and persistence. The protein encoded by Rv0132c has a predicted N–terminal signal sequence and is annotated as an F 420 –dependent glucose-6-phosphate dehydrogenase. Here we show that Rv0132c protein does not have the annotated activity. It does, however, co–purify with F 420 during expression experiments in M. smegmatis . We also show that the Rv0132c–F 420 complex is a substrate for the Tat pathway, which mediates translocation of the complex across the cytoplasmic membrane, where Rv0132c is anchored to the cell envelope. This is the first report of any F 420 –binding protein being a substrate for the Tat pathway and of the presence of F 420 outside of the cytosol in any F 420 –producing microorganism. The Rv0132c protein and its Tat export sequence are essentially invariant in the Mycobacterium tuberculosis complex. Taken together, these results show that current understanding of F 420 biology in mycobacteria should be expanded to include activities occurring in the extra-cytoplasmic cell envelope.