Interaction of lipopolysaccharide with anticoagulant protein tachyplesin from hemocytes of horseshoe crab

在人类中，革兰氏阴性菌感染时释放的脂多糖（LPS）可引起与脓毒性休克相关的严重病理改变。在美国，感染性休克每年造成大约10万人死亡，而且没有专门的药物可用。脂多糖是革兰氏阴性菌外膜外小叶的主要成分。脂质A是脂多糖的膜锚，由一个中心磷酸双糖单元组成，它与多达7个脂肪酸链相连，并参与脂多糖的大部分生物活性。人类的毒性来自于脂多糖或脂质A与膜结合受体或血清蛋白的相互作用，导致促炎介质（如肿瘤坏死因子、白细胞介素-1和白细胞介素-6）的增加。马蹄蟹（Tachypleus tridentatus）是一种古老的蛛形纲动物，具有原始的循环系统，即血淋巴，其中只含有一种细胞，即血细胞。血细胞暴露于细菌内毒素（LPS）导致细胞内凝血级联反应的激活，这是对微生物入侵的防御。该系统由几种蛋白质组成，包括速胞素、速胞素和速胞素，它们可能抑制级联反应。这些是小的碱性蛋白，结合和中和LPS，对革兰氏阴性菌的生长有很强的抗菌作用。在本研究中，我们研究了速胞素与合成脂质A的相互作用，发现脂质A磷酸基团的负电荷与速胞素的正电荷相互作用。两亲环被认为是LPS结合位点的重要基序，可用于设计具有治疗感染性休克特性的分子。利用X-PLOR进行距离几何计算。在速胞素的结构中，我们发现了几丁结合基序。速生抑素的主链结构与钙通道阻滞剂- ω - concontoxin相似。

In humans, lipopolysaccharide (LPS) released during infection by Gram-negative bacteria can cause the severe pathological changes associated with septic shock. In the USA,septic shock is responcible for about 100,000 deaths annually and no specific drugs are available. LPS is the principal component of the outer leaflet of the outer membrane of Gram-negative bacteria. Lipid A,the membrane anchor of LPS,consists of a central phosphodisaccharide unit that is attached to up to seven fatty acid chains and it prossesses most of the biological activities of LPS.The toxicity in humans arises from the interaction of LPS or Lipid A with membrane-bound receptors or serum proteins, leading to an increase in the pro-inflammatory mediators (e.g.tomor necrosis factor, interleukin-1 and interleukin-6).Horseshoe crab (Tachypleus tridentatus) are ancient arachnids that possess a primitive circulatory system, the hemolymph, containing only one kind of cell, the hemocyte. Exposure of hemocytes to bacterial endotoxins (LPS) results in the activation of an intracellular coagulation cascade, a defense against microbial invasion. The system consists of several proteins, including tachyplesin, tachycitin and tachystatin that may inhibit the cascade. These are small basic proteins, which bind and neutralize LPS and have strong anti-bacterial effects on the growth of Gram-negative bacteria.In this study, we studied the interaction of tachyplesin with synthetic lipid A and found that negative charges of phsphate groups of lippid A interact with positive charges of tachyplesin. The amphipathic loop was proposed as an important motif of LPS binding site and may be used in the design of molecules with therapeutic properties against septic shock.distance geometry calculation by using X-PLOR.In the structure of tachycitin, we found the chitinbinding motif like hevein. The main chain structure of tachystatin was similar to that of Ca-channel blocker omega-conotoxin.