title: Structural and functional diversity of bacterial membrane fusion proteins.
abstract: Membrane Fusion Proteins (MFPs) are functional subunits of multi-component transporters that perform diverse physiological functions in both Gram-positive and Gram-negative bacteria. MFPs associate with transporters belonging to Resistance-Nodulation-cell Division (RND), ATP-Binding Cassette (ABC) and Major Facilitator (MF) superfamilies of proteins. Recent studies suggested that MFPs interact with substrates and play an active role in transport reactions. In addition, the MFP-dependent transporters from Gram-negative bacteria recruit the outer membrane channels to expel various substrates across the outer membrane into external medium. This review is focused on the diversity, structure and molecular mechanism of MFPs that function in multidrug efflux. Using phylogenetic approaches we analyzed diversity and representation of multidrug MFPs in sequenced bacterial genomes. In addition to previously characterized MFPs from Gram-negative bacteria, we identified MFPs that associate with RND-, MF- and ABC-type transporters in Gram-positive bacteria. Sequence analyses showed that MFPs vary significantly in size (200-650 amino acid residues) with some of them lacking the signature alpha-helical domain of multidrug MFPs. Furthermore, many transport operons contain two- or three genes encoding distinct MFPs. We further discuss the diversity of MFPs in the context of current views on the mechanism and structure of MFP-dependent transporters.
authors.affiliation: University of Oklahoma Department of Chemistry and Biochemistry 620 Parrington Oval, Room 208 Norman, OK 73019, USA. elenaz@ou.edu
authors.forename: Helen I
authors.initials: HI
authors.lastname: Zgurskaya
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Yamada
authors.forename: Elena B
authors.initials: EB
authors.lastname: Tikhonova
authors.forename: Qiang
authors.initials: Q
authors.lastname: Ge
authors.forename: Ganesh
authors.initials: G
authors.lastname: Krishnamoorthy
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry; D050576:Membrane Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000502:physiology; D010802:Phylogeny; D016415:Sequence Alignment
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D050576:Membrane Fusion Proteins; D008565:Membrane Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C436312:MacA protein, E coli; C077168:emrA protein, Bacteria