Aref, Rasha (1)
Kohler, Sylvia (1)
Hefe (1)
Komplement (1)
Pathogenität (1)
Pneumokokkenoberflächenprotein C (1)
PspC (1)
Repressoren (1)
Vitronektin (1)
complement (1)
pathogenesis (1)
Institut für Mikrobiologie - Abteilung für Genetik & Biochemie (2) (remove)
Comparative analysis of repressor interaction with pleiotropic corepressors Sin3 and Cyc8 in the yeast Saccharomyces cerevisiae (2014)
Aref, Rasha
Transcriptional repression of regulated structural genes in eukaryotes often depends on pleiotropic corepressor complexes. A well-known corepressor conserved from yeast to mammalian systems is Sin3. In addition to Sin3, yeast Cyc8/Tup1 corepressor complex also regulates a diverse set of genes. Both corepressors can be recruited to target genes via interaction with specific DNA-binding proteins, leading to down-regulation of a large number of unrelated structural genes by associated histone deacetylases (HDACs). In vitro interaction studies performed in this work by GST pull-down assays showed that various repressor proteins (such as Whi5, Stb1, Gal80, Rfx1, Ure2, Rdr1, Xbp1, Yhp1, Rox1, Yox1, Dal80 and Mot3) are indeed able to bind pleiotropic corepressors Sin3 and/or Cyc8/Tup1. All repressors interacting with Sin3 contact its paired amphipathic helix domains PAH1 and/or PAH2. Mapping experiments allowed the characterization of minimum repressor domains and to derive a sequence pattern which may be important for repressor interaction with Cyc8 or Sin3. Interactions for some pathway-specific repressors such as Cti6 and Fkh1 have been studied comprehensively; minimal domains of Cti6 and Fkh1 required for interaction with Sin3 have been mapped and subsequently investigated by mutational analysis. In vitro interaction studies could show that amino acids 350-506 of Cti6 bind PAH2 of Sin3. To analyze this Cti6-Sin3 interaction domain (CSID) in more detail, selected amino acids within CSID were replaced by alanine. It turned out that hydrophobic amino acids V467, L481 and L491 L492 L493 are important for Cti6-Sin3 binding. The results of this work also suggest that repression is not executed entirely via Sin3, but rather CSID is also important for contacting pleiotropic corepressor Cyc8. In addition to PAH2 of Sin3, CSID also binds to tetratricopeptide repeats (TPR) of Cyc8. Furthermore, in vitro mapping studies revealed that Fkh1 also binds PAH2 of corepressor Sin3 via its N-terminal domain (aa 51-125). Binding studies with mutagenized Fkh1-Sin3 interaction domain (FSID) showed that Fkh151-125 variants L74A and I78A were unable to bind PAH2 of Sin3. Confirming in vitro studies, Cti6350-506 and Fkh151-125 also displayed in vivo interaction with PAH2 of Sin3 by using the "yeast two -hybrid" system. Chromatin immunoprecipitation (ChIP) analyses have demonstrated Cti6 recruitment to promoters of genes such as RNR3 and SMF3 containing iron responsive elements (IRE). Importantly, Sin3 was also recruited to these promoters but only in the presence of functional Cti6. Similarly, recruitment of Fkh1 and Sin3 to promoters of cell-cycle regulated genes CLB2 and SWI5 was shown. Recruitment of Sin3 was completely Fkh1-dependent. Additional findings of this work shed light on the fact that not only repressor proteins may contact Sin3 but also activator proteins not yet considered for interaction, e. g. specific activators such as Pho4 and Ino2. These findings indicate that Sin3 may fulfill functions beyond acting as a corepressor. In vitro studies on Sin3-Pho4 interaction showed that aa 156-208 of Pho4 are able to bind both PAH1 and PAH2 of Sin3, while an internal region of Ino2 comprising amino acids 119-212 binds to both Sin3 and Cyc8.
Unraveling the interaction of Streptococcus pneumoniae with human vitronectin (2014)
Kohler, Sylvia
Streptococcus pneumoniae (the pneumococcus) is a harmless resident of the human nasopharyngeal cavity, and, in general, every individual is likely to be colonized asymptomatically at least once during life. However, under certain conditions, the bacterium can spread to other tissues and organs causing local, non-invasive infections but also lifethreatening, invasive diseases. Pneumococcal carriage and infection is a highly regulated interplay between pathogen- and host-specific factors and the intimate contact of S. pneumoniae with the surface of the nasopharynx is the crucial step in pneumococcal pathogenesis. Pneumococcal adherence to the respiratory epithelium is mediated by surface-exposed adhesins. These adhesins engage host cell receptors either directly or indirectly by recognizing glycoproteins of the extracellular matrix (ECM) including structural components, such as collagens, laminins, and fibronectins, as well as plasma-derived ECM modulators, like vitronectin and Factor H. Pneumococcal surface protein C (PspC) is a surface-exposed protein and important virulence factor of S. pneumoniae. The multifunctional PspC protein promotes pneumococcal adherence to host cells by interacting with the secretory component of the human polymeric Immunoglobulin receptor of respiratory cells. In addition, PspC facilitates pneumococcal immune evasion by recruiting the complement inhibitor proteins C4b-binding protein (C4BP) and Factor H. Moreover, Factor H bound to the pneumococcal surface promotes bacterial adhesion to human epithelial and endothelial cells. S. pneumoniae also interacts with the human glycoprotein vitronectin. In plasma, monomeric vitronectin regulates thrombosis, fibrinolysis and the terminal complement cascade, while it additionally mediates cell-matrix interactions, cell adhesion and migration in the ECM. It was shown that multimeric, ECM-associated vitronectin facilitates pneumococcal adherence to respiratory epithelial cells. In addition, the interaction of pneumococci with vitronectin promotes their uptake by mucosal epithelial cells via the engagement of the integrin αvβ3 receptor and activation of intracellular signaling pathways culminating in cytoskeletal rearrangements. This study aims to identify and characterize the surface-exposed protein(s) that mediate binding of pneumococci to vitronectin and to elucidate the impact of vitronectin on pneumococcal pathogenesis beyond its function as molecular bridge between pneumococcus and host. Flow cytometric, immunosorbent and surface plasmon resonance experiments revealed that PspC is a vitronectin-binding protein of S. pneumoniae. The specificity of the interaction with vitronectin was confirmed using recombinant PspC proteins and Lactococcus lactis heterologously expressing PspC on their surface. Factor H did not hinder vitronectinbinding to PspC indicating that vitronectin recognizes the central part of PspC. Secretory IgA inhibited but not completely prevented vitronectin-binding to PspC, strongly suggesting that vitronectin binds near, but not directly to, the SC-binding region within the R domain(s) of PspC. In addition, PspC proteins comprising two R domains bound with higher affinity to vitronectin than PspC containing only one R domain, indicating that two interconnected R domains are required for efficient vitronectin-binding. Despite the sequential and structural differences to classical PspC, the PspC-like protein Hic specifically interacted with vitronectin with similar affinity than PspC containing two linked R domains. Binding studies confirmed that Factor H interacts with the very N-terminal region of Hic showing high sequence homology to classical PspC proteins, while vitronectin recognizes an adjacent region in the N-terminal region of Hic. The studied PspC proteins bound to both soluble and immobilized vitronectin, and the C-terminal heparin-binding domain (HBD3) was identified as PspC-binding motif in soluble vitronectin. However, in its immobilized form, vitronectin likely exposes additional binding sites for PspC since a region N-terminally to the identified HBD3 conferred binding of PspC. Vitronectin inhibits the terminal complement pathway, thereby preventing proinflammatory immune reactions and tissue damage. In general, pneumococci are protected from opsonization and MAC-dependent lysis by their capsule. However, pneumococci in close contact to human cells can become susceptible to complement attack due to reduced amounts of capsule. In addition, they can be severely affected by TCC-induced inflammatory responses. Vitronectin bound to PspC significantly inhibited the formation of terminal complement complexes. Thus, the interaction of PspC with vitronectin might aid in immune evasion of S. pneumoniae by inhibiting complement-mediated lysis and/or suppressing proinflammatory events. In conclusion, the results revealed the multifunctional PspC and Hic as vitronectin-binding proteins and proposed a novel role for the specific interaction of S. pneumoniae with vitronectin in regulating the complement cascade, beside its function as molecular bridge to the respiratory epithelium.