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Peptide Discovered In Scorpion Venom May Hold Key To Secretory Diseases
ScienceDaily (Feb. 18, 2008) — Researchers have discovered a peptide in scorpion venom that may hold the key to understanding and controlling cystic fibrosis and other secretory diseases.
In the December 28 issue of the Journal of Biological Chemistry, an international team of researchers describes how this novel peptide, called GaTx1, can control the movement of ions and water out of cells by interacting with a crucial chloride channel.
\" eptide toxins from scorpions, snakes, snails and spiders paralyze prey by blocking nerve or muscle ion channels so the prey can't get away,\" explained Nael A. McCarty, an associate professor in the Georgia Institute of Technology's School of Biology. \"Those toxins have been enormously useful for studying the potassium, calcium, and sodium channels that they interact with, but this is the first toxin discovered that potently binds to and selectively and reversibly inhibits a chloride channel of known molecular identity.\"
Chloride channels are crucial for secretion in many epithelial tissues, but little has been known about their structures and mechanisms. Researchers do know that chloride channels open to allow millions of chloride ions to travel through them and out of epithelial cells. This movement creates an osmotic gradient that allows water to flow.
For the more than 70,000 people worldwide affected by cystic fibrosis, a lack of water flow in airway cells results in abnormally thick, sticky mucus that commonly causes blockages that obstruct airways and glands. The lack of water flow stems from a problem in a chloride channel called the cystic fibrosis transmembrane conductance regulator (CFTR) protein.
In individuals with cystic fibrosis, the CFTR protein is mutated, often with one or more amino acids deleted, and consequently misfolded. In the most common CFTR mutation leading to cystic fibrosis, the location of the deletion causes the chaperone proteins -- which are responsible for quality assurance within cells -- to bind to the misfolded proteins and discard them from the cell. Loss of CFTR proteins stops water from flowing into or out of the cells, thereby altering the conditions in the airway, leading to cystic fibrosis.
In other diseases, CFTR channels are overactive, which also causes problems. These include secretory diarrhea, a worldwide health concern causing thousands of deaths per year; diarrhea-predominant inflammatory bowel disease; and autosomal dominant polycystic kidney diseases, the fourth leading cause of end-stage renal disease in the United States.
With collaborators at the Hungarian Academy of Sciences, Emory University and the University of Calgary, the researchers used reversed-phase high-performance liquid chromatography (HPLC) to extract the novel GaTx1 peptide from the complex venom of the Giant Israeli Scorpion, Leiurus quinquestriatus hebraeus.
\"We chose this technique because each different peptide has slightly different water solubility and hydrophobicity properties, allowing them to be separated,\" explained Julia Kubanek, an associate professor with joint appointments in the Georgia Tech School of Biology and School of Chemistry and Biochemistry.
Former Emory University graduate student Matthew Fuller and Georgia Tech graduate student Christopher Thompson collected individual peptides separated by the HPLC system and then applied each to chloride channels to see which peptide was responsible for the overall effects of the venom. They discovered a novel peptide that bound to the cytoplasmic side of the CFTR protein and weighed 3.7 kilodaltons -- they called it GaTx1.
The researchers plan to use GaTx1 as a molecular probe to learn more about how chloride channels are structured and regulated. They also plan to study how this peptide can be useful in treating secretory diseases. For people with illnesses like secretory diarrhea, GaTx1 could be used to inhibit the channels from opening, in turn decreasing production of the watery diarrhea that often leads to death in patients suffering from cholera and other diarrheal diseases, said McCarty.
To treat patients with cystic fibrosis, GaTx1 could possibly be used to increase water production, by binding to the chaperone binding sites on the chloride channel. By blocking chaperones from binding, CFTR proteins would not be discarded and thus ions and water would flow from the cells to thin the mucus in the airway, according to McCarty.
\"Even though the channels would be misfolded and probably only function at 50 percent capacity, chloride ions and water would still be transported through the cell,\" said McCarty. \"This is better than the alternative of allowing the chaperones to discard all of the CFTR proteins.\"
McCarty has been studying CFTR for his entire research career and as he moves to a new position as associate professor in pediatrics and senior cystic fibrosis scientist at Emory University, he will continue this work in collaboration with researchers at Georgia Tech.
\"GaTx1 has the potential to be used as a drug to help patients with cystic fibrosis and these other secretory diseases,\" added McCarty. \"My new role at Emory will allow me to conduct pre-clinical studies to explore experimental drug treatment options based on this toxin.\"
This research was funded by the National Institutes of Health, National Science Foundation and Cystic Fibrosis Foundation.
科学日报（08年2月18日）消息：研究人员在蝎子毒液中所发现的肽，或许是理解并控制囊性纤维化及其它分泌腺疾病的关键。12月28日（07年底）发布的“生物化学杂志”上，一个国际性研究小组对这种称为“GaTx1”的新肽的作用机制进行了描述，即，如何通过与一种重要的氯离子通道相互作用来控制离子和水分渗出细胞的活动。
背景资料：
1，蝎子、蛇、蜗牛和蜘蛛可利用自生的肽类毒素阻断猎物神经或肌肉的离子通道，从而让猎物瘫痪，无力逃串。这些毒素因可影响钾、钙、钠通道而早已被广泛研究，但“GaTx1”却是已被发现的，首个可以选择性结合已知分子组成的氯通道的肽类，而且其抑制作用具有可逆性。
2，氯通道对许多上皮组织的分泌作用很重要，但其结构和机制尚了解甚少。研究人员们就知道它可以让数以百万计的氯离子通过，并透过内皮细胞。氯离子运动所产生的渗透梯度又带动了水分子的流动。
3，全世界有7万多人受“囊性纤维化”影响，因为气道细胞缺乏水流而致粘液异常稠厚，所以通常会造成气道及腺体阻塞。水流缺乏源于一种叫做“囊性纤维化跨膜传导调节蛋白”（CFTR protein）的氯通道异常。
4，囊性纤维化者CFTR蛋白变异，通常出现一个或更多的氨基酸缺失并因此错误折叠。最常见导致囊性纤维化的变异CFTR中，缺失位点产生蛋白伴侣（其是细胞内质量保证的主要责任者），可与错误折叠蛋白相结合，并将之丢弃出细胞。CFTR蛋白缺乏，使水分不能自由出入细胞，因而改变了气道环境，导致囊性纤维化。
5，另一些疾病中，CFTR通道活性异常增高，同样也导致一些问题。包括：分泌性腹泻——一个每年导致数以万计病人死亡的世界范围的健康忧患；以腹泻为主的炎性肠病；以及常染色体显性遗传性多囊肾病——美国终末期肾病的第4大病因。
研究人员：生物技术大学乔治亚学院的副教授Nael A. McCarty；乔治亚生物技术大学、化学与生物化学大学共同聘任的副教授Julia Kubanek；匈牙利科学院、埃默里大学、加利尔大学的研究人员；前埃默大学研究生Matthew Fulle与乔治亚技术大学研究生Christopher Thompson；等。
PS: McCarty整个职业生涯都在研究CFTR，目前已是埃默大学儿童及年长者囊性纤维化疾病方面的副教授级科学家，他将继续与乔治亚技术大学的研究人员们合作研究下去。
研究资金：由美国国立卫生研究院、美国国家科学基金与囊性纤维化基金提供。
研究策略：
因为，不同肽的水溶性和疏水性有细微差别，使得它们能够被分离。通过反相高效液相色谱法（HPLC系统），从巨大的以色列蝎子的毒液复合物中提纯出该名为“GaTx1”的新肽。（提纯到各种肽后，）将分离出的单一肽采集起来，将其分别应用于氯通道，以观察到底是哪个肽产生了整个毒素的效应。从而发现了这种称为“GaTx1”的新肽，它结合在CFTR的细胞质侧，分子量为3.7千道尔顿。
研究展望：
1，将“GaTx1”作为分子探针，以了解更多关于氯道构成及控制方面的内容。
2，将该肽用于治疗分泌腺疾病。如对于分泌性腹泻的患者，“GaTx1”可以用于抑制通道的开启，进而减少常致腹泻疾病（如霍乱）患者死亡的水样腹泻物的生成。
3，将该肽用于治疗囊性纤维化病人。通过将“GaTx1”与氯通道蛋白伴侣结合位点相结合，阻断伴侣蛋白，CFTR蛋白就不再会被丢弃出细胞，因此离子和水分就会从细胞里流出稀释气道粘液。尽管通道仍会错误折叠，也可能只有50%功能量，但氯离子及水分仍然可以被转送到细胞外。这比让伴侣蛋白选择性丢弃所有的变异CFTR蛋白要好。
4，GaTx1有可能被作为治疗囊性纤维化及其它分泌腺疾病患者的药物。开发基于该毒素的，实验性药物治疗选择的临床前研究，有望开展。 |
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发表于 2008-2-28 08:05:19