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      Structure-based discovery of inhibitors of the YycG histidine kinase: New chemical leads to combat Staphylococcus epidermidis infections


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          Coagulase-negative Staphylococcus epidermidis has become a major frequent cause of infections in relation to the use of implanted medical devices. The pathogenicity of S. epidermidis has been attributed to its capacity to form biofilms on surfaces of medical devices, which greatly increases its resistance to many conventional antibiotics and often results in chronic infection. It has an urgent need to design novel antibiotics against staphylococci infections, especially those can kill cells embedded in biofilm.


          In this report, a series of novel inhibitors of the histidine kinase (HK) YycG protein of S. epidermidis were discovered first using structure-based virtual screening (SBVS) from a small molecular lead-compound library, followed by experimental validation. Of the 76 candidates derived by SBVS targeting of the homolog model of the YycG HATPase_c domain of S. epidermidis, seven compounds displayed significant activity in inhibiting S. epidermidis growth. Furthermore, five of them displayed bactericidal effects on both planktonic and biofilm cells of S. epidermidis. Except for one, the compounds were found to bind to the YycG protein and to inhibit its auto-phosphorylation in vitro, indicating that they are potential inhibitors of the YycG/YycF two-component system (TCS), which is essential in S. epidermidis. Importantly, all these compounds did not affect the stability of mammalian cells nor hemolytic activities at the concentrations used in our study.


          These novel inhibitors of YycG histidine kinase thus are of potential value as leads for developing new antibiotics against infecting staphylococci. The structure-based virtual screening (SBVS) technology can be widely used in screening potential inhibitors of other bacterial TCSs, since it is more rapid and efficacious than traditional screening technology.

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          We present an automatic method for docking organic ligands into protein binding sites. The method can be used in the design process of specific protein ligands. It combines an appropriate model of the physico-chemical properties of the docked molecules with efficient methods for sampling the conformational space of the ligand. If the ligand is flexible, it can adopt a large variety of different conformations. Each such minimum in conformational space presents a potential candidate for the conformation of the ligand in the complexed state. Our docking method samples the conformation space of the ligand on the basis of a discrete model and uses a tree-search technique for placing the ligand incrementally into the active site. For placing the first fragment of the ligand into the protein, we use hashing techniques adapted from computer vision. The incremental construction algorithm is based on a greedy strategy combined with efficient methods for overlap detection and for the search of new interactions. We present results on 19 complexes of which the binding geometry has been crystallographically determined. All considered ligands are docked in at most three minutes on a current workstation. The experimentally observed binding mode of the ligand is reproduced with 0.5 to 1.2 A rms deviation. It is almost always found among the highest-ranking conformations computed.
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            Aminoglycoside antibiotics induce bacterial biofilm formation.

            Biofilms are adherent aggregates of bacterial cells that form on biotic and abiotic surfaces, including human tissues. Biofilms resist antibiotic treatment and contribute to bacterial persistence in chronic infections. Hence, the elucidation of the mechanisms by which biofilms are formed may assist in the treatment of chronic infections, such as Pseudomonas aeruginosa in the airways of patients with cystic fibrosis. Here we show that subinhibitory concentrations of aminoglycoside antibiotics induce biofilm formation in P. aeruginosa and Escherichia coli. In P. aeruginosa, a gene, which we designated aminoglycoside response regulator (arr), was essential for this induction and contributed to biofilm-specific aminoglycoside resistance. The arr gene is predicted to encode an inner-membrane phosphodiesterase whose substrate is cyclic di-guanosine monophosphate (c-di-GMP)-a bacterial second messenger that regulates cell surface adhesiveness. We found that membranes from arr mutants had diminished c-di-GMP phosphodiesterase activity, and P. aeruginosa cells with a mutation changing a predicted catalytic residue of Arr were defective in their biofilm response to tobramycin. Furthermore, tobramycin-inducible biofilm formation was inhibited by exogenous GTP, which is known to inhibit c-di-GMP phosphodiesterase activity. Our results demonstrate that biofilm formation can be a specific, defensive reaction to the presence of antibiotics, and indicate that the molecular basis of this response includes alterations in the level of c-di-GMP.
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              A method to identify protein sequences that fold into a known three-dimensional structure.

              The inverse protein folding problem, the problem of finding which amino acid sequences fold into a known three-dimensional (3D) structure, can be effectively attacked by finding sequences that are most compatible with the environments of the residues in the 3D structure. The environments are described by: (i) the area of the residue buried in the protein and inaccessible to solvent; (ii) the fraction of side-chain area that is covered by polar atoms (O and N); and (iii) the local secondary structure. Examples of this 3D profile method are presented for four families of proteins: the globins, cyclic AMP (adenosine 3',5'-monophosphate) receptor-like proteins, the periplasmic binding proteins, and the actins. This method is able to detect the structural similarity of the actins and 70- kilodalton heat shock proteins, even though these protein families share no detectable sequence similarity.

                Author and article information

                BMC Microbiol
                BMC Microbiology
                BioMed Central (London )
                10 November 2006
                : 6
                : 96
                [1 ]Key laboratory of Medical Molecular Virology of Ministry of Education and Ministry of Pulic Health, Institute of Medical Microbiology and Institutes of Biomedical Sciences, Shanghai Medical School of Fudan University Box 228, Yi Xue Yuan Road 138#, Shanghai 200032, PR China
                [2 ]Drug Discovery and Design Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Graduate School of Chinese Academy of Sciences, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, 65 Zuchongzhi Road, Shanghai 201203, PR China
                [3 ]Infection Microbiology Group, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark
                [4 ]Genetics of Bacterial Genomes, CNRS URA 2171, Institut Pasteur, 28 rue du Docteur Roux, 75724, Paris Cedex 15, France
                Copyright © 2006 Qin et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                : 1 July 2006
                : 10 November 2006
                Research Article

                Microbiology & Virology
                Microbiology & Virology


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