The Function Of Staphylococcus Aureus Superantigen-like Protein SSL12、13、14

Staphylococcus aureus(S.aureus)is a widespread Gram-positive pathogen,which can cause a variety of diseases including fasciitis,sepsis and endocarditis,threatening the life of the host.In order to escape the clearance of the host immune system,S.aureus secretes a variety of virulence factors to interfere with the normal function of the host immune system.Among all kinds of virulence factors,Staphylococcal super antigen like proteins(SSLs)play an important role.SSLs are named as super antigen like proteins because their structure and sequence are highly similar to staphylococcal superantigen proteins.In previous studies,SSLs play a variety of functions by recognizing different host receptor proteins.For example,SSL7 can bind IgA,which hinders the binding of IgA to FCαRI,thus inhibiting the classical pathway of complement activation;SSL 10 can combine with IgG,and also proved to interact with factor Xa to inhibit the fction of coagulation system.However,some superantigen like proteins,including SSL12,SSL13 and SSL14,are still unknown.Among them SSL13 is supposed to interact with MMP26.Matrix metalloproteinases(MMPs)are a class of important zinc dependent proteases in the process of extracellular matrix remodeling,which widely exist in a variety of cells.Their substrates cover the main components of extracellular matrix and are important hydrolases for degradation of extracellular matrix.MMP26 play an important role in the remodeling of extracellular matrix in the growth and development of organisms,as well as pathological damage and repair in diseases.MMP26 family members also participate in many physiological and pathological processes,such as embryonic development,organ formation,tissue damage repair,migration and chemotaxis of immune cells and so on.MMP26 was found in 2001,and its function is not clear.Current studies suggest that MMP26 is related to angiogenesis and wound healing.In the first chapter of this paper,in order to identify the interaction proteins of SSL12,SSL13 and SSL14 in human serum and explore their structure,function and molecular mechanism,SSL12,SSL13 and SSL14 proteins were recombined and purified in E.coli,and the crystal screening was carried out.In the CNBr pull-down of SSLs with human serum,it was found that SSLs could bind to a variety of proteins with potential interaction in human serum,MMP26,a member of matrix metalloproteinase family,was selected as the research object because of other members of the family had precedent of interactions with interaction with SSL family proteins and shows a potential interaction with SSL13 in previous studies.It was verified by gelatin zymography that MMP26 has the ability to degrade gelatin,and this enzyme activity will be inhibited by SSL13.This phenomenon provides a new example for the interaction between MMP family and SSL family proteins,a new idea for the study of MMP protein inhibitors,determines the function of SSL13 and fills the gap in the study of SSLs protein function,and provides a new clue for the pathogenesis of S.aureus.Nuclear membrane is an important structural difference between prokaryotic cells and eukaryotic cells.The existence of nuclear membrane makes cells separate the substances in cytoplasm and nucleus in a relatively independent system,and plays an important role in regulating cell function,the nuclear fiber layer plays an important role in connecting the heterochromatin with the nuclear membrane,and a variety of proteins on it provide sites for chromatin to anchor on the nuclear fiber layer.LBR is an important component of inner nuclear membrane proteins.Its Tudor domain implies that LBR can recognize histone methylation sites,which are important for the formation of heterochromatin.Therefore,it has guiding significance to study LBR and analyze its interaction with histone methylation sites,and provide a new example for the recognition pattern of histone methylation sites by Tudor domain.In the second chapter of this paper,the truncated protein of Tudor domain of Lamin B receptor(LBR)was recombined and expressed in vitro by E.coli Expression System,and the co crystallization of the truncated protein and H4K20me2 was attempted,but no suitable crystal for diffraction was obtained.The following work will explore the structure and recognition mode of the complex,and futher explore the Tudor domain Pattern recognition mechanism of histone post-translational modifications.