Study On The Structure And Function Of Staphylococcus Aureus SdrC Protein

Staphylococcus aureus,a Gram-positive(G+)pathogenic bacteria that is widespread in the population,can cause a range of diseases,such as epidermal infections,endocarditis,and osteomyelitis.Cell wall-anchored(CWA)protein is a type of Staphylococcus aureus surface protein.It can use a microbial surface component that recognizes host surface molecules to mediate some of the adhesion mechanisms that help bacteria attached to the host cell surface.SdrC(serine-aspartate repeat-containing protein C)is a member of the CWA family whose main function is to promote SdrC protein-mediated biofilm formation so that to facilitate bacterial proliferation on the host cell surface.?-neurexin,which is derived from human neuronal cells,inhibits SdrC protein-mediated biofilm formation after binding to SdrC protein and slows the infection of S.aureus to the host.The molecular mechanism of its infection was not very clear.At present,the study of SdrC protein function mainly refers to its functional domain,the functional domain of SdrC is A domain,including N1,N2 and N3 subdomains,the N1 domain always cleavaged in solution,therefore in this study,the SdrCN2N3 protein was expressed using the heterologous expression system of E.coli,and the homogeneity of the protein was obtained by Ni-NTA and gel filtration chromatography.The crystal of SdrCN2N3 protein was obtained by gas phase diffusion method and the structure of SdrC was solved by X-ray crystallography.Analysing the overall structure of SdrC,we can find that the SdrC protein crystal structure is composed of two molecules of SdrCN2N3 protein,forming an interaction between the two molecules interface,N2 and N3 domains are composed of multiple ?-sheet,N2 and N3 forms a DE variant(Dev)-IgG-like fold in the same manner as the MSCRAMM(Microbial Surface Component Recognizing Adhesive Matrix Molecule)protein within the CWA protein family.In vitro,the aggregation state of SdrCN2N3 protein was confirmed by molecular size exclusion chromatography(SEC-MALS)technique.We also test the aggregation status of SdrC A and SdrCAB1.The results showed that all the different forms of SdrC Proteins exist as monomers in solution.While studying the formation of SdrC protein dimers,we also investigated the interaction between SdrC and the ?-neurexin derived peptide(Nrx18).The GST-pull down and ITC assays did not detect the interaction between them.Analysis of the reasons may include the following:First,in vitro GST-pull down and ITC experimental,the solution environment is not conducive to the interaction between them;Second,the SdrC protein are truncated fragments,non-integral fragments,Considering that other domains of the protein will affect its interaction with Nrx18;thirdly,the concentration of SdrC protein and Nrx18 was not explored when verifying the interaction.The biological function of SdrC protein is to promote the formation of bacterial biofilms,which depend on the dimerization of SdrC protein.By analyzing the structure of SdrC protein as a two-body structure,it provides a basis for promoting the formation of bacterial biofilm by SdrC protein.The structure analysis of SdrCN2N3 also provides the basis for the study of the structure of Nrxl 8 and SdrC protein complexes,and further complements the study of the structure of MSCRAMM protein family.