Structure-function studies on IL-18, IL-18 binding proteins and receptors

描述（由申请人提供）：白细胞介素-18 （IL-18）是一种促炎细胞因子，属于白细胞介素-1 （IL-1）超家族。它在宿主对微生物的防御中起着重要作用，但也有助于几种炎症性疾病的发病机制，包括类风湿关节炎、感染性休克和克罗恩病。IL-18信号通过其细胞表面与受体(IL-18R) α亚基结合而启动，随后受体β亚基募集形成三元信号复合物。IL-18的活性在体内受天然拮抗剂IL-18结合蛋白（IL-18BP）通过负反馈机制调控。痘病毒，包括天花（天花）病毒，也表达功能性IL-18BP同源物以逃避il -18介导的宿主免疫应答。因此，IL-18、IL-18R和IL-18BP是有吸引力的靶点，用于开发治疗炎性或感染性疾病的激动剂，其中表明IL-18活性下调或上调。然而，对IL-18如何激活其受体以及IL-18BP如何抑制IL-18缺乏深入的了解。我们建议确定IL-18与IL-18R或IL-18BP的各种蛋白复合物的晶体结构，并根据结构信息进行功能研究。此外，我们将进行基于结构的IL-18变体设计，这些变体可以作为一种更有效的细胞因子，能够逃避痘病毒il - 18bp的中和，或者作为一种能够阻断IL-18活性的受体拮抗剂。目的1。探讨il - 18bp中和IL-18的分子机制。目标2。确定IL-18特异性识别IL-18R 1亚基的分子机制。目标3。确定IL-18触发IL-18R1和2个亚基异二聚化的分子机制。本应用程序的目的是通过结合生物物理和生化方法，包括x射线晶体学，表面等离子体共振（SPR）和IL-18生物测定，详细表征IL-18复合物的集合。实现这一目标是实现我们了解IL-18如何激活其受体启动细胞信号传导以及IL-18BP如何调节这种活性的长期目标的重要的第一步。这项研究获得了额外的维度。由于目标蛋白具有重要的医学相关性，我们的研究将为设计选择性抑制剂提供一个平台，这些抑制剂最终可能被开发成针对许多人类疾病的新疗法。公共卫生相关性：我们在此的贡献有望提供IL-18BP和IL-18R对IL-18的详细分子识别。这一贡献具有重要意义，因为它将填补我们目前对IL-18激活途径的认识空白，并将为如何调节IL-18活性提供重要线索。它可能有利于开发针对某些自身免疫性疾病和炎症性疾病的治疗方法，开发针对其他传染病和癌症的免疫疗法以及打击生物恐怖主义的努力。

DESCRIPTION (provided by applicant): Interleukin-18 (IL-18) is a pro-inflammatory cytokine that belongs to the interleukin-1 (IL-1) superfamily. It plays an important role in host defense against microbes but also contributes to pathogenesis of several inflammatory diseases, including rheumatoid arthritis, septic shock and Crohn's disease. IL-18 signaling is initiated by its cell-surface binding to the receptor (IL-18R) alpha subunit, followed by the recruitment of the receptor beta subunit to form a ternary signaling complex. IL-18 activities are regulated in vivo by a naturally occurring antagonist, the IL-18 binding protein (IL-18BP) through a negative feedback mechanism. Poxviruses, including the smallpox (variola) virus, also express functional IL-18BP homologues to evade IL-18-mediated host immune responses. IL-18, IL-18R and IL-18BP are therefore attractive targets for developing therapeutics agonist inflammatory or infectious diseases where down- or up-modulating IL-18 activities is indicated. However, there is a lack of thorough understanding of how IL-18 activates its receptor and how IL-18BP inhibits IL-18. We propose to determine the crystal structures of various protein complexes of IL-18 with IL-18R or IL-18BP and perform functional studies based on the structural information. In addition, we will perform structure-based design of IL-18 variants that may either serve as a more effective cytokine capable of evading the neutralization of poxvirus IL-18BPs, or as a receptor antagonist capable of blocking IL-18 activities. Aim 1. To determine the molecular mechanism by which IL-18BPs neutralize IL-18. Aim 2. To determine the molecular mechanism by which IL-18 specifically recognizes 1 subunit of IL-18R. Aim 3. To determine the molecular mechanism by which IL-18 triggers the hetero-dimerization of IL-18R1 and 2 subunits. The objective of this application is the detailed characterization of a collection of IL-18 complexes by a combination of biophysical and biochemical methods, including x-ray crystallography, Surface Plasmon Resonance (SPR) and IL-18 bioassay. Accomplishing this objective is an important first step for achieving our long-term goal of understanding how IL-18 activates its receptors to initiate cell signaling and how this activity is regulated by IL-18BP.This research obtains/assumes extra dimensions. Since the targeted proteins are of significant medical relevance, our studies will provide a platform for designing selective inhibitors that may ultimately be developed into new therapeutics against a number of human diseases. Public Health Relevance: Our contribution here is expected to provide detailed molecular recognition of IL-18 by IL-18BP and IL-18R. This contribution is significant because it will fill the gap of our current knowledge on IL-18 activation pathway, and will provide important clues on how to modulate IL-18 activity. It may benefit efforts in developing treatments against some autoimmune and inflammatory diseases, in developing immunotherapies against other infectious diseases and cancer and in combating bioterrorism.