Bacterial tRNA-guanine transglycosylase (Tgt) is involved in the biosynthesis of the modified tRNA nucleoside queuosine present in the anticodon wobble position of tRNAs specific for aspartate, asparagine, histidine and tyrosine. Inactivation of the tgt gene leads to decreased pathogenicity of Shigella bacteria. Therefore, Tgt constitutes a putative target for Shigellosis drug therapy. Since only active as homodimer, interference with dimer-interface formation may, in addition to active-site inhibition, provide further means to disable this protein. A cluster of four aromatic residues seems important to stabilize the homodimer. We mutated residues of this aromatic cluster and analyzed each exchange with respect to dimer and thermal stability or enzyme activity applying native mass spectrometry, thermal shift assay, enzyme kinetics, and X-ray crystallography. Our structural studies indicate strong influence of pH on homodimer stability. Obviously, protonation of a histidine within the aromatic cluster promotes the collapse of an essential structural motif within the dimer interface at slightly acidic pH.

Mechanistic insights into protein-ligand interactions can yield chemical tools for modulating protein function and enable their use for therapeutic purposes.For the homodimeric enzyme tRNA-guanine transglycosylase (TGT), ap utative virulence target of shigellosis,l igand binding has been shown by crystallography to transform the functional dimer geometry into an incompetent twisted one.H owever,c rystallographic observation of both end states does neither verify the ligandinduced transformation of one dimer into the other in solution nor does it shed light on the underlying transformation mechanism. We addressed these questions in an approachthat combines site-directed spin labeling (SDSL) with distance measurements based on pulsed electron-electron double resonance (PELDOR or DEER) spectroscopy. We observed an equilibrium between the functional and twisted dimer that depends on the type of ligand, with ap yranose-substituted ligand being the most potent one in shifting the equilibrium towardt he twisted dimer.O ur experiments suggest ad issociation-association mechanism for the formation of the twisted dimer upon ligand binding.

The intestinal disease shigellosis caused by Shigella bacteria affects over 120 million people annually. There is an urgent demand for new drugs as resistance against common antibiotics emerges. Bacterial tRNA-guanine transglycosylase (TGT) is a druggable target and controls the pathogenicity of Shigella flexneri. We report the synthesis of sugar-functionalized lin-benzoguanines addressing the ribose-33 pocket of TGT from Zymomonas mobilis. Ligand binding was analyzed by isothermal titration calorimetry and X-ray crystallography. Pocket occupancy was optimized by variation of size and protective groups of the sugars. The participation of a polycyclic water-cluster in the recognition of the sugar moiety was revealed. Acetonide-protected ribo- and psicofuranosyl derivatives are highly potent, benefiting from structural rigidity, good solubility, and metabolic stability. We conclude that sugar acetonides have a significant but not yet broadly recognized value in drug development.

Anomeric spirohydantoin derivatives from monosaccharides are known for various biological properties. We describe herein the synthesis of the 3-spirohydantoin derivatives of D-allose and D-ribose. The key step is the stereoselective glyco-alpha-aminonitrile formation from ulose derivatives of D-glucose and D-xylose using titanium tetra-isopropoxide as a mild and efficient catalyst. Target compounds were synthesized from these intermediates. The glucidic moiety was partially or totally deprotected under acidic conditions. These new heterocyclic monosaccharidic derivatives are potent glycogen phosphorylase inhibitors.

Nhẫn thạch là câu chuyện về sự bất bình đẳng giới, là tiếng kêu giải phóng phụ nữ, ở Afghan- istan hay một nơi nào đó trên thế giới. Số phận những người phụ nữ được thể hiện bằng ngôn từ mạnh mẽ, vô cùng trần trụi và chua xót. Trong đó, những người phụ nữ phải phục tùng những người đàn ông (cha, chồng, con của mình) vô điều kiện. Thông qua câu chuyện người phụ nữ chăm sóc người chồng bị đạn găm vào gáy phải sống đời thực vật; thông qua huyền thoại về nhẫn thạch- hòn đá đen ma thuật, tác giả đã bày ra trước mắt người đọc định kiến xã hội về tiết hạnh của người phụ nữ, quan niệm tình yêu, hôn nhân, gia đình, về chiến tranh và cả những ẩn ức tôn giáo, tính dục. Bên cạnh đó, tác phẩm còn thể hiện một nền văn hóa Hồi giáo đậm nét, hiển nhiên bởi Atiq Rahimi viết về Afghanistan- đất nước mà Hồi giáo ngự trị.