PDF(Pubmed)
Abstract：
Tick saliva injected into the vertebrate host contains bioactive anti-proteolytic proteins from the cystatin family; however, the molecular basis of their unusual biochemical and physiological properties, distinct from those of host homologs, is unknown. Here, we present Ricistatin, a novel secreted cystatin identified in the salivary gland transcriptome of Ixodes ricinus ticks. Recombinant Ricistatin inhibited host-derived cysteine cathepsins and preferentially targeted endopeptidases, while having only limited impact on proteolysis driven by exopeptidases. Determination of the crystal structure of Ricistatin in complex with a cysteine cathepsin together with characterization of structural determinants in the Ricistatin binding site explained its restricted specificity. Furthermore, Ricistatin was potently immunosuppressive and anti-inflammatory, reducing levels of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α and nitric oxide in macrophages; IL-2 and IL-9 levels in Th9 cells; and OVA antigen-induced CD4+ T cell proliferation and neutrophil migration. This work highlights the immunotherapeutic potential of Ricistatin and, for the first time, provides structural insights into the unique narrow selectivity of tick salivary cystatins determining their bioactivity.
摘要：
注射到脊椎动物宿主中的滴答唾液含有来自胱抑素家族的生物活性抗蛋白水解蛋白；然而，它们不寻常的生化和生理特性的分子基础，与宿主同源物不同，是未知的。这里,我们介绍了Ricistin,在蓖麻蜱的唾液腺转录组中发现的一种新型分泌的胱抑素。重组Ricistin抑制宿主来源的半胱氨酸组织蛋白酶和优先靶向内肽酶，而对外肽酶驱动的蛋白水解只有有限的影响。与半胱氨酸组织蛋白酶复合物中的Ricistin的晶体结构的确定以及Ricistin结合位点中结构决定子的表征解释了其有限的特异性。此外，Ricistin具有有效的免疫抑制和抗炎作用，降低促炎细胞因子IL-6，IL-1β，巨噬细胞中的TNF-α和一氧化氮；Th9细胞中的IL-2和IL-9水平；以及OVA抗原诱导的CD4T细胞增殖和中性粒细胞迁移。这项工作突出了Ricistin的免疫治疗潜力，第一次,提供了对tick唾液胱抑素决定其生物活性的独特窄选择性的结构见解。
