Activation of Fc receptors by innate acute phase proteins

固有急性期蛋白激活 Fc 受体

• 批准号: 8946339
• 负责人: PETER D. SUN
• 金额: $ 36.8万
• 依托单位: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8946339
• 关键词: Acute-Phase Proteins; Amyloid; Antigen-Antibody Complex; Autoimmune Diseases; Bacteria; Binding; Binding Sites; Biological Assay; C-terminal; Cells; Charge; Competitive Binding; Complement; Complement 1q; Complex; Dissociation; Excision; Face; Family; Family member; Fc Receptor; Glycosaminoglycans; Goals; Heparin; High Density Lipoproteins; Human; Humoral Immunities; IgA receptor; Immunoglobulin A; Immunoglobulin G; Infection; Inflammation; Inflammatory; Inflammatory Response; Ligands; Mediating; Mediator of activation protein; N-terminal; Natural Immunity; Parasitic infection; Pathway interactions; Peptides; Phagocytosis; Phosphorylation; Plasma Proteins; Production; Protomer; Receptor Activation; Role; Secondary Amyloidosis; Serum; Serum amyloid A protein; Site; Solutions; Structure; Surface; TNF gene; Tail; Virus Diseases; Work; amyloid formation; base; combat; crosslink; cytokine; design; emergency service responder; insight; macrophage; neutrophil; novel; novel therapeutics; receptor; receptor binding; research study

Recent evidence suggests that pentraxins interact with Fc receptors raising the possiblity of cross interaction between the complement and the Fc receptor mediated pathways. We are investigating the interaction between SAP/CRP and Fc receptors and determine the structure of their complex. We have recently determined the crystal structure of human SAP in complex with FcRIIa. The 1:1 receptor-SAP recognition is predominantly mediated through the interactions of the ridge helix from two separate SAP protomers with the D1 and D2 domains of the Fc receptor. The complex structure between human SAP and FcRIIa reveals a diagonally bound receptor on each SAP pentamer. Mutational analysis suggests a conserved receptor recognition among pentraxins. The shared binding site for SAP and IgG results in their competition to FcR binding and the inhibition of immune complex-mediated phagocytosis by soluble pentraxins. These results establish the role of innate pentraxins in the FcgR pathway, and have novel therapeutic implications for autoimmune diseases.Unexpectedly, the SAP binding site on FcRIIa overlaps partially with the IgG binding site on the receptor. The solution-based binding experiments confirmed that SAP and CRP competed against IgG for the binding to FcRs. Solutuion binding experiments showed that pentraxins recognize various FcRs and activate FcR-mediated phagocytosis and cytokine secretion. Moreover, soluble SAP and CRP inhibited significantly the immune complex-mediated phagocytosis, indicating a regulatory function for this family of plasma proteins. The result highlights the importance of pentraxins in interfacing between the innate and humoral immunities and suggests new therapeutic applications for pentraxins in autoimmune diseases. We recently identified the major IgA receptor, FcRI as a ligand for pentraxins. We conclude through competitive binding and mutational analysis that CRP binds to a distinct site on FcRI from that of IgA, and that the recognition involves the effector face of CRP in a region overlapping with its C1q and FcR binding site. Furthermore, CRP crosslinking of FcRI resulted in ERK phosphorylation, degranulation and cytokine production in FcRI transfected RBL cells. In neutrophils, CRP binding induced FcRI surface expression and TNF- secretion, and CRP-opsonized bacteria triggered phagocytosis. The impact of this work is two folds. First, the discovery that pentraxins activate FcRI reveals a novel function for pentraxins in inflammation. It implicates a potential pentraxin-mediated synergistic activation of various Fc receptors in neutrophil and macrophage-mediated inflammatory responses. This is particular so since neutrophils and macrophages are the first responders of infection and inflammation. Second, our finding also highlights the innate aspect of antibody receptors that are mediators of humoral immunity. As pentraxins, such as CRP, are acute phase proteins whose expressions are upregulated during infections, we are investigating the potential role of CRP in Fc receptor activations during parasitic and viral infections. Serum Amyloid A (SAA) represents an evolutionarily conserved family of inflammatory acute phase proteins. It is also a major constituent of secondary amyloidosis. To understand its function and structural transition to amyloid, we determined the first structure of human SAA1.1 in two crystal forms, representing a prototypic member of the family. Native SAA1.1 exists as a hexamer with subunits displaying a unique four-helix bundle fold stabilized by its long C-terminal tail. The structural-based mutational studies revealed two positive charge clusters, near the center and apex of the hexamer, are involved in SAA association with heparin. The binding of high density lipoprotein (HDL) involves only the apex region of SAA and can be inhibited by heparin. Peptide amyloid formation assays identified the N-terminal helix 1 and helix 3 as amyloidogenic peptides of SAA1.1. Both peptides are secluded in the hexameric structure of SAA1.1, suggesting the native SAA as non-pathogenic. Further, dissociation of the SAA hexamer appears insufficient to initiate amyloidogenic transition, and proteolytic cleavage or removal of the C-terminal tail of SAA resulted in formation of various sized structural aggregates containing 5 nm regular repeating protofibril-like units. The combined structural and functional studies provide mechanistic insights to the pathogenic contribution of glycosaminoglycan in SAA1.1-mediated AA amyloid formation.

最近的证据表明，五肽与FC受体相互作用，从而增加了补体和FC受体介导的途径之间交叉相互作用的可能性。 我们正在研究SAP/CRP和FC受体之间的相互作用，并确定其复合物的结构。我们最近确定了与FCRIIA复合物中人类SAP的晶体结构。 1：1受体识别的识别主要是通过从两个单独的SAP原始物与FC受体的D1和D2结构域的脊螺旋相互作用来介导的。人类SAP和FCRIIA之间的复杂结构揭示了每个SAP Pentamer上的对角线受体。 突变分析表明五肽之间的受体识别是保守的。用于SAP和IgG的共享结合位点导致其与FCR结合的竞争，并抑制可溶性五肽的免疫复合物介导的吞噬作用。这些结果确定了先天五肽在FCGR途径中的作用，并对自身免疫性疾病具有新的治疗意义。毫无指示，FCRIIA上的SAP结合位点与受体上的IgG结合位点部分重叠。基于溶液的结合实验证实，SAP和CRP与IgG竞争与FCR的结合。溶质结合实验表明，五肽素识别各种FCR，并激活FCR介导的吞噬作用和细胞因子分泌。 此外，可溶性SAP和CRP显着抑制了免疫复合物介导的吞噬作用，表明该血浆蛋白家族的调节功能。 结果凸显了五卫蛋白在与先天和体液免疫之间接触中的重要性，并提出了五型五肽在自身免疫性疾病中的新治疗应用。 我们最近将主要的IgA受体FCRI确定为五肽的配体。我们通过竞争性结合和突变分析得出结论，CRP与IgA的FCRI上的不同位点结合，并且该识别涉及与其C1Q和FCR结合位点重叠的区域中CRP的效应子面。 此外，FCRI的CRP交联导致FCRI转染的RBL细胞的ERK磷酸化，脱粒和细胞因子产生。 在中性粒细胞中，CRP结合诱导的FCRI表面表达和TNF分泌，以及CRP揭示的细菌引发了吞噬作用。这项工作的影响是两个折。 首先，发现五肽激活FCRI的发现揭示了pentraxins在炎症中的新功能。 这意味着潜在的pentraxin介导的在中性粒细胞和巨噬细胞介导的炎症反应中各种FC受体的协同激活。这是特别的，因为中性粒细胞和巨噬细胞是感染和炎症的第一反应者。 其次，我们的发现还突出了抗体受体的先天性，这些抗体受体是体液免疫的介体。 由于五肽（例如CRP）是急性相蛋白，其表达在感染过程中被上调，我们正在研究CRP在寄生和病毒感染期间FC受体激活中的潜在作用。 血清淀粉样蛋白A（SAA）代表炎症急性相蛋白的进化保守家族。 它也是继发性淀粉样变性的主要组成部分。 为了了解其功能和结构过渡到淀粉样蛋白，我们以两种晶体形式确定了人类SAA1.1的第一个结构，代表了家族的原型成员。 本机SAA1.1作为六聚体和亚基的存在，显示出独特的四螺旋束折叠，其长C末端尾巴稳定。 基于结构的突变研究表明，在六聚体的中心和顶点附近的两个正电荷簇参与了与肝素的SAA关联。高密度脂蛋白（HDL）的结合仅涉及SAA的先端区域，肝素可以抑制。肽淀粉样蛋白形成测定法将N末端螺旋1和螺旋3鉴定为SAA1.1的淀粉样蛋白生成肽。 这两种肽均在SAA1.1的六聚体结构中隔离，表明天然SAA为非致病性。 此外，SAA六聚体的解离似乎不足以启动淀粉样蛋白生成过渡，蛋白水解裂解或移除SAA的C末端尾巴导致形成了各种大小的结构聚集体，这些结构聚集体含有5 nm规则重复的原子质类似原子纤维样单位。 结合结构和功能研究为SAA1.1介导的AA淀粉样蛋白形成中糖胺聚糖的致病作用提供了机械见解。