二氢蝶呤醛缩酶(DHNA)对于微生物中叶酸的生物合成至关重要。没有哺乳动物的对应物,DHNA是抗微生物剂的有吸引力的靶标。幽门螺杆菌感染发生在人类胃中,占世界人口的50%以上,但是感染的一线疗法正面临着迅速增加的抵抗力。迫切需要新型抗生素,关于潜在目标的结构信息对其至关重要。我们已经确定了幽门螺杆菌DHNA(HpDHNA)与蝶呤分子(HpDHNA:Pterin)复合的晶体结构,分辨率为1.49。HpDHNA:Pterin复合物在晶体中形成四聚体。还通过动态光散射在溶液中观察到四聚体,并通过小角度X射线散射证实。迄今为止,除了一个报道的DHNA结构外,所有结构都是八聚体复合物。作为唯一的例外,无配体结核分枝杆菌DHNA(apo-MtDHNA)在晶体中形成四聚体,但其活性位点仅部分形成。相比之下,四聚体HpDHNA:Pterin复合物具有良好形成的活性位点。每个活性位点容纳一个蝶呤分子,但是活性位点的出口被两个氨基酸残基阻断,接触距离为5.2。相比之下,金黄色葡萄球菌DHNA(SaDHNA)中相应的接触距离是其大小的两倍,范围从9.8到10.5,对于无配体酶,底物复合物,复杂的产品,和抑制剂复合物。这种大的接触距离表明SaDHNA的活性位点是敞开的。我们建议这种同工酶特异性接触距离(ISCD)是DHNA活性位点的特征。HpDHNA和SaDHNA结构的比较分析提示了开发同工酶特异性抑制剂的基于片段的策略。
Dihydroneopterin aldolase (DHNA) is essential for folate biosynthesis in microorganisms. Without a counterpart in mammals, DHNA is an attractive target for antimicrobial agents. Helicobacter pylori infection occurs in human stomach of over 50% of the world population, but first-line therapies for the infection are facing rapidly increasing resistance. Novel antibiotics are urgently needed, toward which structural information on potential targets is critical. We have determined the crystal structure of H. pylori DHNA (HpDHNA) in complex with a pterin molecule (HpDHNA:Pterin) at 1.49-Å resolution. The HpDHNA:Pterin complex forms a tetramer in crystal. The tetramer is also observed in solution by dynamic light scattering and confirmed by small-angle X-ray scattering. To date, all but one reported DHNA structures are octameric complexes. As the only exception, ligand-free Mycobacterium tuberculosis DHNA (apo-MtDHNA) forms a tetramer in crystal, but its active sites are only partially formed. In contrast, the tetrameric HpDHNA:Pterin complex has well-formed active sites. Each active site accommodates one pterin molecule, but the exit of active site is blocked by two amino acid residues exhibiting a contact distance of 5.2 Å. In contrast, the corresponding contact distance in Staphylococcus aureus DHNA (SaDHNA) is twice the size, ranging from 9.8 to 10.5 Å, for ligand-free enzyme, the substrate complex, the product complex, and an inhibitor complex. This large contact distance indicates that the active site of SaDHNA is wide open. We propose that this isozyme-specific contact distance (ISCD) is a characteristic feature of DHNA active site. Comparative analysis of HpDHNA and SaDHNA structures suggests a fragment-based strategy for the development of isozyme-specific inhibitors.