title: Crystal structure of the periplasmic component of a tripartite macrolide-specific efflux pump.
abstract: In Gram-negative bacteria, type I protein secretion systems and tripartite drug efflux pumps have a periplasmic membrane fusion protein (MFP) as an essential component. MFPs bridge the outer membrane factor and an inner membrane transporter, although the oligomeric state of MFPs remains unclear. The most characterized MFP AcrA connects the outer membrane factor TolC and the resistance-nodulation-division-type efflux transporter AcrB, which is a major multidrug efflux pump in Escherichia coli. MacA is the periplasmic MFP in the MacAB-TolC pump, where MacB was characterized as a macrolide-specific ATP-binding-cassette-type efflux transporter. Here, we report the crystal structure of E. coli MacA and the experimentally phased map of Actinobacillus actinomycetemcomitans MacA, which reveal a domain orientation of MacA different from that of AcrA. Notably, a hexameric assembly of MacA was found in both crystals, exhibiting a funnel-like structure with a central channel and a conical mouth. The hexameric MacA assembly was further confirmed by electron microscopy and functional studies in vitro and in vivo. The hexameric structure of MacA provides insight into the oligomeric state in the functional complex of the drug efflux pump and type I secretion system.
authors.affiliation: College of Pharmacy and Research Institute for Drug Development, Pusan National University, Busan 609-735, Korea.
authors.forename: Soohwan
authors.initials: S
authors.lastname: Yum
authors.forename: Yongbin
authors.initials: Y
authors.lastname: Xu
authors.forename: Shunfu
authors.initials: S
authors.lastname: Piao
authors.forename: Se-Hoon
authors.initials: SH
authors.lastname: Sim
authors.forename: Hong-Man
authors.initials: HM
authors.lastname: Kim
authors.forename: Wol-Soon
authors.initials: WS
authors.lastname: Jo
authors.forename: Kyung-Jin
authors.initials: KJ
authors.lastname: Kim
authors.forename: Hee-Seok
authors.initials: HS
authors.lastname: Kweon
authors.forename: Min-Ho
authors.initials: MH
authors.lastname: Jeong
authors.forename: Hyesung
authors.initials: H
authors.lastname: Jeon
authors.forename: Kangseok
authors.initials: K
authors.lastname: Lee
authors.forename: Nam-Chul
authors.initials: NC
authors.lastname: Ha
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016976:Aggregatibacter actinomycetemcomitans / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018942:Macrolides / Q000378:metabolism; D050576:Membrane Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; C083497:AcrA protein, E coli; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D008074:Lipoproteins; C436312:MacA protein, E coli; D018942:Macrolides; D050576:Membrane Fusion Proteins; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; D011994:Recombinant Proteins