RESUMO
The structure determination of the recombinant form of BclA, the major protein component of Bacillus anthracis exosporium, involved soaking in a high concentration of potassium iodide as the means of obtaining a good-quality heavy-atom derivative. The data to 2 angstroms resolution collected on a laboratory source were of sufficient quality to allow successful phasing and chain tracing by automated methods.
Assuntos
Halogênios/química , Glicoproteínas de Membrana/química , Esporos Bacterianos/química , Sequência de Bases , Primers do DNA , Modelos Moleculares , Conformação ProteicaRESUMO
The lethal disease anthrax is propagated by spores of Bacillus anthracis, which can penetrate into the mammalian host by inhalation, causing a rapid progression of the disease and a mostly fatal outcome. We have solved the three-dimensional structure of the major surface protein BclA on B. anthracis spores. Surprisingly, the structure resembles C1q, the first component of complement, despite there being no sequence homology. Although most assays for C1q-like activity, including binding to C1q receptors, suggest that BclA does not mimic C1q, we show that BclA, as well as C1q, interacts with components of the lung alveolar surfactant layer. Thus, to better recognize and invade its hosts, this pathogenic soil bacterium may have evolved a surface protein whose structure is strikingly close to a mammalian protein.
Assuntos
Bacillus anthracis/metabolismo , Glicoproteínas de Membrana/química , Animais , Dicroísmo Circular , Complemento C1q/química , Cristalografia por Raios X , Relação Dose-Resposta a Droga , Humanos , Modelos Moleculares , Ligação Proteica , Conformação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Proteínas Recombinantes/química , Propriedades de Superfície , Tensoativos/química , Temperatura , Fator de Necrose Tumoral alfa/química , Raios UltravioletaRESUMO
The Bacillus subtilis LrpC protein belongs to the Lrp/AsnC family of transcriptional regulators. It binds the upstream region of the lrpC gene and autoregulates its expression. In this study, we have dissected the mechanisms that govern the interaction of LrpC with DNA by electrophoretic mobility shift assay, electron microscopy, and atomic force microscopy. LrpC is a structure-specific DNA binding protein that forms stable complexes with curved sequences containing phased A tracts and wraps DNA to form spherical, nucleosome-like structures. Formation of such wraps, initiated by cooperative binding of LrpC to DNA, results from optimal protein/protein interactions specified by the DNA conformation. In addition, we have demonstrated that LrpC constrains positive supercoils by wrapping the DNA in a right-handed superhelix, as visualized by electron microscopy.