Structural biology of soft tick complement inhibitor (OMCI) alone and in complex with C5

补语系统是一组近似地。30种蛋白质共同作用，形成抵御寄生虫和其他病原体入侵的前线防御系统。至于所有的蛋白质，我们只有通过对它们详细的原子结构的了解，才能真正了解这些蛋白质对抗入侵的方式。然而，许多补体系统蛋白质很难在这种详细程度上进行研究，因此我们几乎没有这个重要生物系统中心组成部分的原子水平结构信息。大多数寄生虫试图通过表达专门作用于干扰这些防御的分子来克服补体系统建立的防御。这项应用寻求使用扁虱表达的抗补体分子来增加我们对扁虱蛋白如何工作的理解(通过解决这种抑制剂的原子结构)，并通过准确地发现扁虱抑制剂如何阻止其正确功能，来增加我们对关键补体成分之一--一种名为C5的蛋白质的理解。朝着这一目标迈出的关键的第一步是确定C5和抑制剂之间的相互作用部位。我们将使用各种不同的生化方法来确定相互作用的部位。包括(1)确定C5的哪些片段与抑制剂结合，(2)研究C5与抑制剂与结合C5的补体组分竞争时的相互作用，以及(3)在C5中引入阻止抑制剂结合的单一氨基酸变化。有了这些数据和材料(C5的纯化片段)，我们将试图确定C5(或其很大一部分)和TICK抑制剂之间的复合体的原子结构，以便为我们提供一个框架，以解释我们的生化数据和对C5生物功能的先验知识。

The complement system is a group of approx. 30 proteins that act together to form a frontline defence against invasion by parasites and other pathogens. As for all proteins we can only really understand the ways in which these proteins act to combat invasion by knowledge of their detailed, atomic, structure. However, many of the complement system proteins are difficult to study at this level of detail and we therefore have little atomic level structural information for the central components of this important biological system. Most parasites attempt to overcome the defence mounted by the complement system by expressing molecules that act specifically to interfere with these defences. This application seeks to use an anti-complement molecule expressed by a tick to increase our understanding both of how the tick protein works (by solving the atomic structure of this inhibitor) and also to increase our understanding of one of the key complement components, a protein called C5, by discovering precisely how the tick inhibitors prevent its correct functioning. A vital first step towards this aim is the identification of the site of interaction between C5 and the inhibitor. We will use a variety of different biochemical methods to identify the site of interaction. Including (1) determining which fragments of C5 bind to the inhibitor, (2) studying the interaction between C5 and inhibitor in competition with complement components which bind to C5, and (3) introducing single amino acid changes to C5 that prevent the inhibitor binding. Armed with these data and materials (purified fragments of C5) we will attempt to determine an atomic structure for a complex between C5 (or a significant part of it) and the tick inhibitor to give us a framework on which to interpret our biochemical data and prior knowledge of the biological function of C5.