Nucleotide-free Crystal Structure of Nucleotide-binding Domain 1 from Human ABCC1 Supports a ‘General-Base Catalysis’ Mechanism for ATP Hydrolysis

Abstract

ATP-binding cassette (ABC) transporters are molecular motors that transport substrates through biological membranes, using the energy of ATP binding and hydrolysis to foster a series of conformational changes that follow the alternating access mechanism principles. While this general scheme of substrate transport is well accepted, details about the ATP hydrolysis mechanism itself are still a matter of debate. Decades of biochemical and structural studies have identified well-conserved key residues involved in the enzymatic reaction, but their actual role, or order in the hydrolytic process, differ according to the mechanism involved. Here, we investigate the fundamental mechanisms of ATP hydrolysis, by reporting the nucleotide-free structure of the N-terminal nucleotide-Binding Domain (NBD1) of human Multidrug Resistance Protein 1 (MRP1/ABCC1), a transporter of chemotherapeutic drugs. Comparison with the nucleotide-bound structure clearly identified movements of H827 associated with nucleotide binding and release of the active site. These results, put in the context of other structural information and mutational studies of ABC transporters, support the general-base catalysis mechanism for ATP hydrolysis for ABCC1.