The most fundamental property of biological membranes is to serve as a selective barrier, allowing the penetration of only solutes of certain classes. The structural basis of these functions will be investigated by using several experimental systems from bacteria. (1) The outer membrane, located outside the peptidoglycan layer and the cytoplasmic membrane of gram-negative bacteria, is an ideal model membrane for the study of this type, because its functions are very simple in that it allows mainly passive and facilitated diffusion processes. The diffusion of hydrophilic solutes are mediated by porin and other specific channels, and the properties of these channels will be characterized. Areas that will be emphasized will include the voltage- and pressure-mediated closing of the porin channel, the identity and properties of porin channels in Pseudomonas aeruginosa, and the functional architecture of specific channels such as the phage lambda receptor (maltoporin) channel. In addition, unusual specific transport systems that require the collaboration of TonB protein will be studied by using a newly developed assay. Finally, the molecular basis of the unusually low permeability of lipid bilayer region of the outer membrane will be studied by utilizing intact cells, planar bilayers, and bilayer vesicles. The results of these studies are of great medical interest, as most of the antibiotic-resistant bacterial pathogens causing hospital-acquired infections are bacteria covered with outer membranes of low permeability. They can thus suggest ways to produce more effective antibiotics that can overcome this barrier. (2) The mycobacterial cell wall is rich in lipidic constituents, and was recently shown to act as an extremely effective permeability barrier. We will study how hydrophilic molecules diffuse across this barrier. If porin-like proteins can be identified and characterized, this will again suggest ways of improving the penetration of antibiotics and chemotherapeutic agents into these bacteria, especially """"""""atypical"""""""" mycobacteria well-known for their antibiotic resistance and their capability of causing intractable secondary infections in many AIDS patients. (3) The molecular mechanism of transport of maltose across the cytoplasmic membrane of Escherichia coli will be studied. This system is of interest not only because it is a highly complex and efficient transport machinery, but also its component proteins share a strong sequence homology with the P-glycoprotein that pumps out anti-cancer drugs from some of the tumor cells.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Method to Extend Research in Time (MERIT) Award (R37)
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University of California Berkeley
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Kinana, Alfred D; Vargiu, Attilio V; May, Thithiwat et al. (2016) Aminoacyl ?-naphthylamides as substrates and modulators of AcrB multidrug efflux pump. Proc Natl Acad Sci U S A 113:1405-10
Li, Xian-Zhi; Pl├ęsiat, Patrick; Nikaido, Hiroshi (2015) The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria. Clin Microbiol Rev 28:337-418
Soparkar, Ketaki; Kinana, Alfred D; Weeks, Jon W et al. (2015) Reversal of the Drug Binding Pocket Defects of the AcrB Multidrug Efflux Pump Protein of Escherichia coli. J Bacteriol 197:3255-64
Nobre, Thatyane M; Martynowycz, Michael W; Andreev, Konstantin et al. (2015) Modification of Salmonella Lipopolysaccharides Prevents the Outer Membrane Penetration of Novobiocin. Biophys J 109:2537-2545
Vargiu, Attilio V; Ruggerone, Paolo; Opperman, Timothy J et al. (2014) Molecular mechanism of MBX2319 inhibition of Escherichia coli AcrB multidrug efflux pump and comparison with other inhibitors. Antimicrob Agents Chemother 58:6224-34
Sugawara, Etsuko; Nikaido, Hiroshi (2014) Properties of AdeABC and AdeIJK efflux systems of Acinetobacter baumannii compared with those of the AcrAB-TolC system of Escherichia coli. Antimicrob Agents Chemother 58:7250-7
Kinana, Alfred D; Vargiu, Attilio V; Nikaido, Hiroshi (2013) Some ligands enhance the efflux of other ligands by the Escherichia coli multidrug pump AcrB. Biochemistry 52:8342-51
Sugawara, Etsuko; Nagano, Keiji; Nikaido, Hiroshi (2012) Alternative folding pathways of the major porin OprF of Pseudomonas aeruginosa. FEBS J 279:910-8
Kim, Hong-Suk; Nikaido, Hiroshi (2012) Different functions of MdtB and MdtC subunits in the heterotrimeric efflux transporter MdtB(2)C complex of Escherichia coli. Biochemistry 51:4188-97
Vargiu, Attilio V; Nikaido, Hiroshi (2012) Multidrug binding properties of the AcrB efflux pump characterized by molecular dynamics simulations. Proc Natl Acad Sci U S A 109:20637-42

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