1403 Quorum sensing: How bacteria can coordinate activity and synchronize their response to external signals?
Zhi Li and Satish K. Nair
Bacteria are able to communicate with each other using small molecule signaling compounds, in response to changes in their external environment. This process is called quorum sensing, and is used by bacterial species to coordinate their behavior with changes in population. This review describes the biochemical basis for this signaling process, with special emphasis on providing an understanding of the molecular details of how quorum signals are generated and recognized in Gram-negative bacteria.
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1456 Lanthanide binding and IgG affinity construct: Potential applications in solution NMR, MRI and luminescence microscopy
Adam W. Barb, Tienhuei Grace Ho, Heather Flanagan-Steet, and James H. Prestegard
Peptides having high affinity for lanthanide ions provide versatile probes of molecular structure and biological function when incorporated in proteins of interest. They provide distance and angle dependent structural information at an atomic level through paramagnetic relaxation enhancement of NMR resonances. They can provide high sensitivity contrast for optical microscopy and magnetic resonance imaging. This article describes engineering of a lanthanide binding peptide into a protein that, in turn, binds to a domain of immunoglobulin G. Preliminary applications point the way to future use in the characterization of glycoproteins of the immune system and antibody directed imaging.
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1467 pH effects on binding between the anthrax protective antigen and the host cellular receptor CMG2
Maheshinie Rajapaksha, Scott Lovell, Blythe E. Janowiak, Kiran K. Andra, Kevin P. Battaile, and James G. Bann
How does the anthrax toxin protective antigen (PA), a protein necessary for anthrax pathogenesis, bind to the host cellular receptor capillary morphogenesis protein 2 (CMG2)? To address this question, Rajapaksha, et al. studied the kinetics of binding and dissociation of PA to CMG2 as a function of pH, and correlated this information to the X-ray crystal structures of PA at high and low pH. Our studies suggest that binding becomes progressively stronger at lower pH values, and is likely due to an increase in the flexibility of the PA protein as the pH is lowered, allowing access to a more bound-like conformation.
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1528 Engineered variants of InlB with an additional leucine-rich repeat discriminate between physiologically relevant and packing contacts in crystal structures of the InlB:MET complex
Hartmut H. Niemann, Ermanno Gherardi, Willem M. Bleymüller, and Dirk W. Heinz
Predicting the correct quaternary arrangement based on protein crystal structures remains a formidable computational challenge for low affinity complexes, as crystal contacts may represent crystallization artifacts rather than functional contacts. Here the authors probe the relevance of a crystallographic assembly between a human cell surface receptor and its agonistic ligand from a pathogenic bacterium. Insertion of an additional repeat unit into the curved bacterial repeat protein retains the high-affinity 1:1 complex with the receptor while specifically disrupting a higher order assembly under scrutiny. Cellular assays show that this assembly, although predicted to be stable, is not the signaling active complex on cells.
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