Structure And Function Of Streptococcus Pneumoniae SP0498Big,Saccharomyces Cerevisiae SWI1ARID And Human SUV39H1Chromo Domains

This dissertation focuses on the structure and molecular mechanism of Streptococcus pneumoniae SPO498Big, Saccharomyces cerevisiae SWI1ARID and human SUV39H1chromo domains.1. Streptococcus pneumoniae is a pathogen causing acute respiratory infection of some severe diseases in human. The solution structure of a bacterial immunoglobulin-like (Big) domain from a putative S. pneumoniae surface protein SP0498was determined by NMR spectroscopy. SP0498Big domain adopts an eight-β-strand barrel-like fold, which is different in some aspects from the two-sheet sandwich-like fold of the canonical Ig-like domains. Intriguingly, we identified that the SPO498Big domain was a Ca2+-binding domain. The structure of the Big domain is different from those of the well known Ca2+-binding domains, therefore revealing a novel Ca2+-binding module. Furthermore, we identified the critical residues responsible for the binding to Ca2+. We are the first to report the interactions between the Big domain and Ca2+in terms of structure, suggesting an important role of the Big domain in many essential calcium-dependent cellular processes such as pathogenesis.2. SWI1is a subunit of the SWI/SNF complex involved in chromatin remodeling. It contains an AT-rich interaction domain (ARID) which has the potential DNA binding activity. We determined the solution structure of the SWI1ARID domain from Saccharomyces cerevisiae by NMR spectroscopy. Yeast SWI1ARID domain is composed of seven α-helices, six of which are conserved among the ARID family. In addition, the DNA binding activity of the SWI1ARID domain was confirmed by chemical shift perturbation assay. Similar to its human homologous, the yeast SWI1ARID domain binds DNA non-specifically. Study of the structure of SWI1ARID domain and exploration of its nonspecific interactions with DNA provide us more details about the structure of ARID family and its DNA-binding properties. This will also provide us more acknowledgment about the involvement of SWI/SNF chromatin remodeling complex in the regulation of gene transcription.3. SUV39H1, the first identified histone lysine methyltransferase in human, is involved in chromatin modification and gene regulation. SUV39H1contains a chromodomain in its N-terminus, which potentially plays a role in methyl-lysine recognition and SUV39H1targeting. The structure of the chromodomain of human SUV39H1was determined by X-ray crystallography. The SUV39H1chromodomain displays a generally conserved structure fold compared with other solved chromodomains. However, different from other chromodomains, the SUV39H1chromodomain possesses a much longer helix at its C-terminus. Furthermore, the SUV39H1chromodomain was shown to recognize trimethylated histone H3K9(H3K9me3) specifically by surface plasmon resonance (SPR) assays. Study of the structure of SUV39H1chromodomain and identification of its specific binding to H3K9m3will help us to reveal more details about its role in the histone modification and gene silence.