Bidirectional communication between nucleotide and substrate binding sites in a type IV multidrug ABC transporter

ATP-binding cassette (ABC) transporters use ATP to transport substrates across cellular membranes. In type IV ABC transporters, including many multidrug resistance (MDR) pumps, communication between the nucleotide-binding domains (NBDs) and transmembrane domains (TMDs) occurs via intracellular coupling helices. However, the precise mechanism of interdomain crosstalk and coordination between the ATP and substrate binding sites remain unclear. Combining nuclear magnetic resonance (NMR) spectroscopy, Hydrogen-Deuterium eXchange Mass Spectrometry (HDX-MS), photo-induced electron-transfer fluorescence correlation spectroscopy (PET-FCS) and functional assays, we identified a conserved cluster of residues at the NBD/TMD interface of the bacterial MDR transporter BmrA. This cluster is crucial for transporter function and relays nucleotide and substrate binding between the two domains via coupling helix 2. Mutations impact both local and global transporter dynamics. Our findings reveal a novel interdomain communication pathway in type IV ABC transporters, shedding light on the intricate coupling mechanisms that enable the coordination of these molecular machines.