Structural And Functional Studies Of Sa240from Staphylococcus Aureus And The Preliminary Structural Study Of Histone Demethylase Mina53

(1) Ribose pyranose catalyzes the conversion of ribose from the pyranose to furanose form. Sequence alignment reveals that ribose pyranose is conserved in a large number of bacteria. The crystal structure of RbsD from Bacillus subtilis (BsRbsD) has been solved in2003. BsRbsD assembled into a pentameric ring structure in one crystallographic asymmetric unit, with adjacent pentamers forming a decamer. The ribose binding site of BsRbsD was identified at the interfacce of two neighboring monomers.Staphylococcus aureus is a Gram-positive bacterium and an important human and animal pathogen. Sa240from Staphylococcus aureus is a ribose pyranase homolog. Here, we report the crystal structures of apo-Sa240and Sa240-ribose complex. The overall structure of Sa240was a αβα sandwich. In one asymmetric unit, there were four Sa240molecules, which formed by two dimmers related by a non-crystallographic2-fold rotational symmetry. Each of the four molecules had two interfaces with neighboring subunits. The interface of AB or CD had a buried surface of about1080A2and the interaction was strong enough to form a stable dimmer. The interface of AC or BD only had a buried surface of about300A2, which may be a result of crystal packing. Some amino acid residues at the interface between adjacent BsRbsD monomers are not conserved in Sa240, which disrupt the hydrophobic and salt bridge interactions between neighboring Sa240subunits at the same interface. The C-terminus conformation of Sa240was different from the C-terminus of BsRbsD. All the factors mentioned above prevented Sa240from forming a pentameric ring structure similar to BsRbsD, and are consistent with the observation that Sa240exists in dimeric form in solution. In the Sa240-ribose complex structure, ribose was clearly identified in its pyranose form indicating that Sa240was inactive in its dimeric form. This is thought to be because the sugar binding site was formed by a single Sa240molecule without an additional histidine residue from the adjacent subunits, which is known to be important for the enzymatic activity of ribose pyranases. The inactive Sa240dimer may be the intermediates from which Sa240dacamer can form under some conditions in vivo. Based on structure analysis and the enzyme mechanism analysis, we propose that the enzymatic activity of ribose pyranase is dependent on the protein’s oligomeric form and that Sa240is inactive in its dimeric state. (2) Mina53(Myc-induced nuclear antigen with a molecular mass of53kDa) is a direct target of MYC and involved in mammalian cell proliferation, highly expressed in oesophageal squamous carcinoma, colon cancer and non-small-cell lung cancer. Mina53exerts oncogenic property in NIH/3T3cells. Mina53contains a JmjC domain and suppresses formation of tri-methyl lysine9of histone H3. Here we report the preliminary structural study of mina53. We cloned and purified a fragment of mina53(amino acids29-465). Mina53exists as a homodimer in solution. Although we crystallized this fragment of mina53, the crystal is of poor diffraction quality despite various attempts to optimize the crystallization condition and can not be used for X-ray diffraction data collection.