Glutamine residues in Q-loops of multidrug resistance protein MRP1 contribute to ATP binding via interaction with metal cofactor

► The Q residues in Q-loops of MRP1 interact with Mg++ and contribute to Mg · ATP-binding. ► Mutations eliminating amide group significantly decreased Mg · ATP binding. ► Mutations eliminating amide group significantly increased the Km and Vmax values. ► The Q residues in Q-loops of MRP1 may not play a crucial role in ATP hydrolysis. ► May not play crucial roles in transmitting the conformational changes between domains.