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      Structural Insights into a Novel Interkingdom Signaling Circuit by Cartography of the Ligand-Binding Sites of the Homologous Quorum Sensing LuxR-Family

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          Recent studies have identified a novel interkingdom signaling circuit, via plant signaling molecules, and a bacterial sub-family of LuxR proteins, bridging eukaryotes and prokaryotes. Indeed pivotal plant-bacteria interactions are regulated by the so called Plant Associated Bacteria (PAB) LuxR solo regulators that, although closely related to the quorum sensing (QS) LuxR family, do not bind or respond to canonical quorum sensing N-acyl homoserine lactones (AHLs), but only to specific host plant signal molecules. The large body of structural data available for several members of the QS LuxR family complexed with different classes of ligands (AHLs and other compounds), has been exploited to dissect the cartography of their regulatory domains through structure-based multiple sequence alignments, structural superimposition and a comparative analysis of the contact residues involved in ligand binding. In the absence of experimentally determined structures of members of the PAB LuxR solos subfamily, an homology model of its prototype OryR is presented, aiming to elucidate the architecture of its ligand-binding site. The obtained model, in combination with the cartography of the regulatory domains of the homologous QS LuxRs, provides novel insights into the 3D structure of its ligand-binding site and unveils the probable molecular determinants responsible for differences in selectivity towards specific host plant signal molecules, rather than to canonical QS compounds.

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          Most cited references 54

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          The Protein Data Bank.

          The Protein Data Bank (PDB; ) is the single worldwide archive of structural data of biological macromolecules. This paper describes the goals of the PDB, the systems in place for data deposition and access, how to obtain further information, and near-term plans for the future development of the resource.
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            Inference of macromolecular assemblies from crystalline state.

            We discuss basic physical-chemical principles underlying the formation of stable macromolecular complexes, which in many cases are likely to be the biological units performing a certain physiological function. We also consider available theoretical approaches to the calculation of macromolecular affinity and entropy of complexation. The latter is shown to play an important role and make a major effect on complex size and symmetry. We develop a new method, based on chemical thermodynamics, for automatic detection of macromolecular assemblies in the Protein Data Bank (PDB) entries that are the results of X-ray diffraction experiments. As found, biological units may be recovered at 80-90% success rate, which makes X-ray crystallography an important source of experimental data on macromolecular complexes and protein-protein interactions. The method is implemented as a public WWW service.
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              The SWISS-MODEL workspace: a web-based environment for protein structure homology modelling.

              Homology models of proteins are of great interest for planning and analysing biological experiments when no experimental three-dimensional structures are available. Building homology models requires specialized programs and up-to-date sequence and structural databases. Integrating all required tools, programs and databases into a single web-based workspace facilitates access to homology modelling from a computer with web connection without the need of downloading and installing large program packages and databases. SWISS-MODEL workspace is a web-based integrated service dedicated to protein structure homology modelling. It assists and guides the user in building protein homology models at different levels of complexity. A personal working environment is provided for each user where several modelling projects can be carried out in parallel. Protein sequence and structure databases necessary for modelling are accessible from the workspace and are updated in regular intervals. Tools for template selection, model building and structure quality evaluation can be invoked from within the workspace. Workflow and usage of the workspace are illustrated by modelling human Cyclin A1 and human Transmembrane Protease 3. The SWISS-MODEL workspace can be accessed freely at

                Author and article information

                Int J Mol Sci
                Int J Mol Sci
                International Journal of Molecular Sciences
                Molecular Diversity Preservation International (MDPI)
                October 2013
                15 October 2013
                : 14
                : 10
                : 20578-20596
                [1 ]Institute of Crystallography, National Research Council, Trieste Outstation, Area Science Park-Basovizza, S.S. n° 14 Km 163.5, I-34149 Trieste, Italy; E-Mail: sonia.covaceuszach@
                [2 ]International Centre for Genetic Engineering and Biotechnology, Padriciano 99, I-34149 Trieste, Italy; E-Mail: degrassi@
                [3 ]IBIOBA-CONICET-ICGEB, International Centre for Genetic Engineering and Biotechnology, Scientific and Technological Center, Godoy Cruz 2390, C1425FQD, Buenos Aires, Argentina
                Author notes
                [* ]Authors to whom correspondence should be addressed; E-Mails: venturi@ (V.V.); doriano.lamba@ (D.L.); Tel.: +39-40-3757319 (V.V.); +39-40-3758514 (D.L.); Fax: +39-40-226555 (V.V.); +39-40-9221126 (D.L.).
                © 2013 by the authors; licensee MDPI, Basel, Switzerland

                This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (



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