Structural Study On SafD Adhesion Of Salmonella

As the pathogenic bacteria, Salmonella can cause gastroenteritis and enteric fever in humans and domesticated animals. The first step of Salmonella's invading the host cells is adhering to these cells through the aid of Salmonella's fimbriae. Fimbriae, as the Salmonella's adhering organ, is the thin fiber on the outer surfaces. By looking at the fimbriae under the electron microscope, the fimbriae is composed of many contiguous protein subuints, From the outer membrane of Salmonella, the SafA subunit has been shown to form the main shaft of the fimbriae. According to the scientific material and data, the scientists proposed that the SafD protein should function as the “cap”and sit at the tip of the fimbriae shaft.However, the function, structure, and location of SafD in Saf fimbriae are not known. The hypothesis that SafD may sit at the tip of the fimbriae shaft is only a hypothesis, never has been proved through the scientific research.The analysis of the SafD protein structure is vital to the study of the mechanism of Salmonella's invading the host cells. In the paper, We described the process of cloning, expression and purification of Samonella SafD(31-156)gene, but from the purification result we could know SafD(31-156)protein the gene expressed was unstable. Subsequently, we conducted the experiment of cloning, expression and purification of SafD(31-156)-DSC gene, and from the purification result we could know SafD(31-156)-DSC protein the gene expressed was stable. Through the purification we got enough SafD(31-156)-DSC protein for crystallization, achieving >95% purity. We Later performed the experiment of protein crystallization, crystal optimation, diffraction and collection of diffraction data. And finally we analysed the data and successfully got SafD(31-156)-DSC protein structure of 2.0 ? resolution. We completely stated the whole process of structural biology studies of SafD protein in this paper. The analysed three-dimensional structure of SafD protein might be useful to design novel subunit vaccines and rapid diagnostic kits against most common Salmonella virulence strains.