The glycyl-radical enzyme 2-ketobutyrate formate-lyase, TdcE, interacts specifically with the formate-translocating FNT-channel protein FocA.

Formate is a major product of mixed-acid fermentation in . Because formate can act as an uncoupler at high concentration it must be excreted from the cell. The FNT (formate-nitrite transporter) membrane channel FocA ensures formate is translocated across the cytoplasmic membrane. Two glycyl-radical enzymes (GREs), pyruvate formate-lyase (PflB) and 2-ketobutyrate formate-lyase (TdcE), generate formate as a product of catalysis during anaerobic growth of . We demonstrate in this study that TdcE, like PflB, interacts specifically with FocA. His-tagged variants of two other predicted GREs encoded in the genome of were over-produced and purified and were shown not to interact with FocA, indicating that interaction with FocA is not a general property of GREs . Together, these data show that only the GREs TdcE and PflB interact with the FNT channel protein and suggest that, like PflB, TdcE can control formate translocation by FocA.