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      Monoclonal antibody targeting the β-barrel assembly machine of Escherichia coli is bactericidal

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          Significance

          The outer membrane of Gram-negative bacteria presents a formidable barrier to the discovery of new antibiotics needed to combat infections by multidrug-resistant bacteria. Targeting essential proteins or processes directly exposed to the environment could bypass this obstacle. Here, we describe a monoclonal antibody that selectively and potently antagonizes BamA, which folds and inserts integral outer membrane β-barrel proteins, by binding to a surface-exposed BamA epitope and, as a result, inhibits bacterial cell growth. Mechanisms of resistance to the antibody reveal that membrane fluidity affects BamA activity. This antibody validates the potential therapeutic strategy of targeting essential, exposed functions and provides a powerful tool for dissecting the fundamental process of folding integral membrane β-barrel proteins in vivo.

          Abstract

          The folding and insertion of integral β-barrel membrane proteins into the outer membrane of Gram-negative bacteria is required for viability and bacterial pathogenesis. Unfortunately, the lack of selective and potent modulators to dissect β-barrel folding in vivo has hampered our understanding of this fundamental biological process. Here, we characterize a monoclonal antibody that selectively inhibits an essential component of the Escherichia coli β-barrel assembly machine, BamA. In the absence of complement or other immune factors, the unmodified antibody MAB1 demonstrates bactericidal activity against an E. coli strain with truncated LPS. Direct binding of MAB1 to an extracellular BamA epitope inhibits its β-barrel folding activity, induces periplasmic stress, disrupts outer membrane integrity, and kills bacteria. Notably, resistance to MAB1-mediated killing reveals a link between outer membrane fluidity and protein folding by BamA in vivo, underscoring the utility of this antibody for studying β-barrel membrane protein folding within a living cell. Identification of this BamA antagonist highlights the potential for new mechanisms of antibiotics to inhibit Gram-negative bacterial growth by targeting extracellular epitopes.

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          Most cited references49

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          Molecular basis of bacterial outer membrane permeability revisited.

          Gram-negative bacteria characteristically are surrounded by an additional membrane layer, the outer membrane. Although outer membrane components often play important roles in the interaction of symbiotic or pathogenic bacteria with their host organisms, the major role of this membrane must usually be to serve as a permeability barrier to prevent the entry of noxious compounds and at the same time to allow the influx of nutrient molecules. This review summarizes the development in the field since our previous review (H. Nikaido and M. Vaara, Microbiol. Rev. 49:1-32, 1985) was published. With the discovery of protein channels, structural knowledge enables us to understand in molecular detail how porins, specific channels, TonB-linked receptors, and other proteins function. We are now beginning to see how the export of large proteins occurs across the outer membrane. With our knowledge of the lipopolysaccharide-phospholipid asymmetric bilayer of the outer membrane, we are finally beginning to understand how this bilayer can retard the entry of lipophilic compounds, owing to our increasing knowledge about the chemistry of lipopolysaccharide from diverse organisms and the way in which lipopolysaccharide structure is modified by environmental conditions.
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            Membrane fluidity and its roles in the perception of environmental signals.

            Poikilothermic organisms are exposed to frequent changes in environmental conditions and their survival depends on their ability to acclimate to such changes. Changes in ambient temperature and osmolarity cause fluctuations in the fluidity of cell membranes. Such fluctuations are considered to be critical to the initiation of the regulatory reactions that ultimately lead to acclimation. The mechanisms responsible for the perception of changes in membrane fluidity have not been fully characterized. However, the analysis of genome-wide gene expression using DNA microarrays has provided a powerful new approach to studies of the contribution of membrane fluidity to gene expression and to the identification of environmental sensors. In this review, we focus on the mechanisms that regulate membrane fluidity, on putative sensors that perceive changes in membrane fluidity, and on the subsequent expression of genes that ensures acclimation to a new set of environmental conditions.
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              Identification of a multicomponent complex required for outer membrane biogenesis in Escherichia coli.

              Gram-negative bacteria have an outer membrane (OM) that functions as a barrier to protect the cell from toxic compounds such as antibiotics and detergents. The OM is a highly asymmetric bilayer composed of phospholipids, glycolipids, and proteins. Assembly of this essential organelle occurs outside the cytoplasm in an environment that lacks obvious energy sources such as ATP, and the mechanisms involved are poorly understood. We describe the identification of a multiprotein complex required for the assembly of proteins in the OM of Escherichia coli. We also demonstrate genetic interactions between genes encoding components of this protein assembly complex and imp, which encodes a protein involved in the assembly of lipopolysaccharides (LPS) in the OM. These genetic interactions suggest a role for YfgL, one of the lipoprotein components of the protein assembly complex, in a homeostatic control mechanism that coordinates the overall OM assembly process.
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                Author and article information

                Journal
                Proc Natl Acad Sci U S A
                Proc. Natl. Acad. Sci. U.S.A
                pnas
                pnas
                PNAS
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                0027-8424
                1091-6490
                3 April 2018
                19 March 2018
                19 March 2018
                : 115
                : 14
                : 3692-3697
                Affiliations
                [1] aDepartment of Infectious Diseases, Genentech Inc. , South San Francisco, CA 94080;
                [2] bDepartment of Protein Analytical Chemistry, Genentech Inc. , South San Francisco, CA 94080;
                [3] cDepartment of Structural Biology, Genentech Inc. , South San Francisco, CA 94080;
                [4] dDepartment of Antibody Engineering, Genentech Inc. , South San Francisco, CA 94080;
                [5] eDepartment of Bioinformatics and Computational Biology, Genentech Inc. , South San Francisco, CA 94080
                Author notes
                1To whom correspondence should be addressed. Email: rutherford.steven@ 123456gene.com .

                Edited by Scott J. Hultgren, Washington University School of Medicine, St. Louis, MO, and approved February 21, 2018 (received for review January 4, 2018)

                Author contributions: K.M.S., M.R.A., H.S., N.N.N., G.N., D. Seshasayee, J.T.K., J.P., P.A.S., and S.T.R. designed research; K.M.S., M.R.A., H.S., N.K.G., D. Sun, N.N.N., R.V., Z.L., N.C., K.S., E.S., D. Seshasayee, J.T.K., P.A.S., and S.T.R. performed research; K.M.S., H.S., N.K.G., D. Sun, N.N.N., R.V., Z.L., N.C., A.T.W., E.S., G.N., D. Seshasayee, J.T.K., P.A.S., and S.T.R. contributed new reagents/analytic tools; K.M.S., M.R.A., H.S., A.T.W., E.S., J.T.K., J.P., P.A.S., and S.T.R. analyzed data; and K.M.S., J.P., and S.T.R. wrote the paper.

                Article
                201800043
                10.1073/pnas.1800043115
                5889671
                29555747
                3cc5dce4-d41f-4d3d-bc1a-67e9616b1a7d
                Copyright © 2018 the Author(s). Published by PNAS.

                This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

                History
                Page count
                Pages: 6
                Categories
                Biological Sciences
                Microbiology

                gram-negative bacteria,β-barrel protein,membrane protein folding,lps,bama

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