RESUMO
Pathogenic bacteria possess adhesion protein complexes that play essential roles in targeting host cells and in propagating infection. Although each family of adhesion proteins is generally associated with a specific human disease, the Dr family from Escherichia coli is a notable exception, as its members are associated with both diarrheal and urinary tract infections. These proteins are reported to form both fimbrial and afimbrial structures at the bacterial cell surface and target a common host cell receptor, the decay-accelerating factor (DAF or CD55). Using the newly solved three-dimensional structure of AfaE, we have constructed a robust atomic resolution model that reveals the structural basis for assembly by donor strand complementation and for the architecture of capped surface fibers.
Assuntos
Adesinas de Escherichia coli/química , Escherichia coli/química , Estrutura Terciária de Proteína , Adesinas de Escherichia coli/genética , Adesinas de Escherichia coli/metabolismo , Sequência de Aminoácidos , Antígenos CD55/química , Antígenos CD55/metabolismo , Cristalografia por Raios X , Escherichia coli/metabolismo , Escherichia coli/patogenicidade , Fímbrias Bacterianas , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Subunidades Proteicas/química , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Alinhamento de Sequência , Ressonância de Plasmônio de SuperfícieRESUMO
Pathogenic Escherichia coli expressing Afa/Dr adhesins are able to cause both urinary tract and diarrheal infections. The Afa/Dr adhesins confer adherence to epithelial cells via interactions with the human complement regulating protein, decay accelerating factor (DAF or CD55). Two of the Afa/Dr adhesions, AfaE-III and DraE, differ from each other by only three residues but are reported to have several different properties. One such difference is disruption of the interaction between DraE and CD55 by chloramphenicol, whereas binding of AfaE-III to CD55 is unaffected. Here we present a crystal structure of a strand-swapped trimer of wild type DraE. We also present a crystal structure of this trimer in complex with chloramphenicol, as well as NMR data supporting the binding position of chloramphenicol within the crystal. The crystal structure reveals the precise atomic basis for the sensitivity of DraE-CD55 binding to chloramphenicol and demonstrates that in contrast to other chloramphenicol-protein complexes, drug binding is mediated via recognition of the chlorine "tail" rather than via intercalation of the benzene rings into a hydrophobic pocket.
Assuntos
Adesinas Bacterianas/química , Adesinas de Escherichia coli/química , Cloranfenicol/química , Proteínas de Escherichia coli/química , Adesinas Bacterianas/metabolismo , Adesinas de Escherichia coli/metabolismo , Antibacterianos/farmacologia , Aderência Bacteriana , Antígenos CD55/química , Cloranfenicol/metabolismo , Cloranfenicol/farmacologia , Clonagem Molecular , Proteínas do Sistema Complemento , Cristalografia por Raios X , Proteínas de Escherichia coli/metabolismo , Humanos , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Ligação Proteica , Conformação Proteica , Estrutura Secundária de Proteína , Ressonância de Plasmônio de Superfície , Raios XRESUMO
Decay-accelerating factor (CD55), a regulator of the alternative and classical pathways of complement activation, is expressed on all serum-exposed cells. It is used by pathogens, including many enteroviruses and uropathogenic Escherichia coli, as a receptor prior to infection. We describe the x-ray structure of a pathogen-binding fragment of human CD55 at 1.7 A resolution containing two of the three domains required for regulation of human complement. We have used mutagenesis to map biological functions onto the molecule; decay-accelerating activity maps to a single face of the molecule, whereas bacterial and viral pathogens recognize a variety of different sites on CD55.
