Structures of a Na+-coupled, substrate-bound MATE multidrug transporter

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Multidrug transporters, including the multidrug and toxic compound extrusion (MATE) family, are crucial for cellular defense against xenobiotics.
• MATE proteins dissipate ion gradients (Na(+) or H(+)) to export diverse drugs, but their transport mechanism remains unclear due to limited structural data.

Purpose of the Study:

• To elucidate the structural basis of substrate recognition and transport mechanism in Na(+)-coupled MATE transporters.
• To provide high-resolution structures of the NorM transporter in complex with various substrates and ions.

Main Methods:

• X-ray crystallography was used to determine the structures of the NorM transporter from Neisseria gonorrheae.
• Structures were obtained for complexes with three substrates (ethidium, rhodamine 6G, tetraphenylphosphonium) and a sodium ion congener (Cs(+)).
• Functional validation involved drug resistance and transport assays.

Main Results:

• Crystal structures revealed a drug-binding cavity with negatively charged residues and limited hydrophobic regions, challenging previous models of multidrug recognition.
• An unusual cation-π interaction was identified in the Na(+)-binding site, located separately from the drug-binding pocket.
• Structural and functional data indicated that Na(+) binding induces conformational changes, rather than direct competition, to drive substrate extrusion.

Conclusions:

• The findings suggest a novel mechanism for Na(+)-coupled MATE transporters where ion binding triggers conformational rearrangements for drug export.
• This mechanism differs from canonical antiport models and provides key insights into multidrug transport.
• The study advances the mechanistic understanding of MATE family transporters and their role in drug resistance.