Cryo-EM Structures of CusA Reveal a Mechanism of Metal-Ion Export

• Published in: mBio Vol. 12; no. 2
• Main Authors: Moseng, Mitchell A, Lyu, Meinan, Pipatpolkai, Tanadet, Glaza, Przemyslaw, Emerson, Corey C, Stewart, Phoebe L, Stansfeld, Phillip J, Yu, Edward W
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 05-04-2021
• Subjects: Binding Sites; Biological Transport; Copper - metabolism; Cryoelectron Microscopy; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli - ultrastructure; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - ultrastructure; Ion Transport; Membrane Transport Proteins - chemistry; Membrane Transport Proteins - ultrastructure; Metals, Heavy - metabolism; Molecular Dynamics Simulation; Protein Binding; Research Article; Silver - metabolism; CusA; efflux pump; resistance-nodulation-cell division; antimicrobial resistance; cryo-EM
• ISSN: 2150-7511; 2150-7511
• DOI: 10.1128/mBio.00452-21

Gram-negative bacteria utilize the resistance-nodulation-cell division (RND) superfamily of efflux pumps to expel a variety of toxic compounds from the cell. The
CusA membrane protein, which recognizes and extrudes biocidal Cu(I) and Ag(I) ions, belongs to the heavy-metal efflux (HME) subfamily of RND efflux pumps. We here report four structures of the trimeric CusA heavy-metal efflux pump in the presence of Cu(I) using single-particle cryo-electron microscopy (cryo-EM). We discover that different CusA protomers within the trimer are able to bind Cu(I) ions simultaneously. Our structural data combined with molecular dynamics (MD) simulations allow us to propose a mechanism for ion transport where each CusA protomer functions independently within the trimer.
The bacterial RND superfamily of efflux pumps mediate resistance to a variety of biocides, including Cu(I) and Ag(I) ions. Here we report four cryo-EM structures of the trimeric CusA pump in the presence of Cu(I). Combined with MD simulations, our data indicate that each CusA protomer within the trimer recognizes and extrudes Cu(I) independently.