Assembly and Channel Opening of Outer Membrane Protein in Tripartite Drug Efflux Pumps of Gram-negative Bacteria

• Published in: The Journal of biological chemistry Vol. 287; no. 15; pp. 11740 - 11750
• Main Authors: Xu, Yongbin, Moeller, Arne, Jun, So-Young, Le, Minho, Yoon, Bo-Young, Kim, Jin-Sik, Lee, Kangseok, Ha, Nam-Chul
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 06.04.2012; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - ultrastructure; Bacterial Pathogenesis; Binding Sites; Crystallography, X-Ray; Drug Resistance, Multiple, Bacterial; Electron Microscopy (EM); Membrane Transport Proteins - chemistry; Membrane Transport Proteins - ultrastructure; MexA; Microscopy, Electron; Models, Molecular; Molecular Sequence Data; Multidrug Transporters; OprM; Pathogenesis; Peptidoglycan - chemistry; Protein Binding; Protein Interaction Domains and Motifs; Protein Multimerization; Protein Structure and Folding; Protein Structure, Quaternary; Pseudomonas aeruginosa; Structural Biology; Surface Properties; TolC; Pathogenesis; MexA; TolC; Structural Biology; Bacterial Pathogenesis; OprM; Electron Microscopy (EM); Multidrug Transporters
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.329375

Gram-negative bacteria are capable of expelling diverse xenobiotic substances from within the cell by use of three-component efflux pumps in which the energy-activated inner membrane transporter is connected to the outer membrane channel protein via the membrane fusion protein. In this work, we describe the crystal structure of the membrane fusion protein MexA from the Pseudomonas aeruginosa MexAB-OprM pump in the hexameric ring arrangement. Electron microscopy study on the chimeric complex of MexA and the outer membrane protein OprM reveals that MexA makes a tip-to-tip interaction with OprM, which suggests a docking model for MexA and OprM. This docking model agrees well with genetic results and depicts detailed interactions. Opening of the OprM channel is accompanied by the simultaneous exposure of a protein structure resembling a six-bladed cogwheel, which intermeshes with the complementary cogwheel structure in the MexA hexamer. Taken together, we suggest an assembly and channel opening model for the MexAB-OprM pump. This study provides a better understanding of multidrug resistance in Gram-negative bacteria. Background:Pseudomonas aeruginosa mainly achieves multidrug resistance by use of the MexAB-OprM pump. Results: We determined the crystal structure of MexA. Electron microscopy work using MexA and OprM reveals that MexA makes a tip-to-tip interaction with OprM. Conclusion: We suggest an assembly and channel opening model for the pump. Significance: This study provides a better understanding of multidrug resistance in Gram-negative bacteria.