Crystal Structure of the Periplasmic Component of a Tripartite Macrolide-Specific Efflux Pump

Crystal Structure of the Periplasmic Component of a Tripartite Macrolide-Specific Efflux Pump
Soohwan YumYongbin XuShunfu PiaoSe-Hoon SimHong-Man KimWol-Soon JoKyung-Jin KimHee-Seok KweonMin-Ho Jeong전혜성Kangseok LeeNam-Chul Ha
multidrug efflux pump; MacA; TolC; AcrA; Gram-negative bacteria
Issue Date
Journal of molecular biology
VOL 387, NO 5, 1286-1297
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 ofMFPs 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.
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