C1q蛋白 来源于正常人血清

C1q 与 C1r、C1s 以及其他稳定蛋白分离后，极易发生聚集。由于众多研究实验室都对其进行分离和研究，因此人们研发了多种缓冲液，用于稳定浓缩态 C1q 并防止其聚集。约有一半的科研人员倾向于在储存缓冲液中使用高盐浓度，另一半则更青睐添加 40% 甘油的缓冲液。 C1q 从混合正常人血浆中纯化得到，是 C1 复合物的组成部分，而该复合物是补体经典激活途径级联反应中的首个补体成分。实际上，C1 是由三种不同蛋白质（C1q、C1r、C1s）通过非共价键组装形成的复合物，其组装过程依赖钙离子。C1q 拥有六个延伸臂，每个臂的末端都有一个结构域，该结构域可与免疫球蛋白的 Fc 结构域结合。当抗体与抗原结合形成免疫复合物时，会发生聚集，使得 C1q 六个臂中的两个或多个臂能够与 IgG 或 IgM 等抗体的 Fc 结构域结合。多个臂与免疫复合物的结合会促使复合物中的两种 C1r 蛋白（蛋白酶原）发生自身激活，产生两种 C1r 蛋白酶，这些蛋白酶会切割并激活复合物中的两种 C1s 蛋白酶原。激活后的 C1s 会切割补体成分 C4，释放出 C4a，并启动 C4b 与激活表面的共价结合。此外，激活后的 C1s 还会切割 C2，C2 切割后产生的较大片段会与结合在表面的 C4b 结合，形成 C4b、C2a 复合物，该复合物即为补体经典激活途径中的 C3/C5 转化酶。 基本参数 消光系数：纯 C1q 在浓度为 1.0mg/ml 时，于 280nm 波长下的消光系数为 0.68。 分子量：410,000 道尔顿（由 18 条链组成）。 防腐剂：无，经 0.22μm 滤膜过滤。 来源：正常人血清（经认证检测证实，乙肝表面抗原（HBsAg）、人类 T 淋巴细胞白血病病毒 Ⅰ/Ⅱ 型（HTLV - Ⅰ/Ⅱ）、梅毒血清学试验（STS）均呈阴性，且抗丙型肝炎病毒（HCV）抗体、抗人类免疫缺陷病毒 Ⅰ 型（HIV - 1）抗体及抗人类免疫缺陷病毒 Ⅱ 型（HIV - Ⅱ）抗体也均为阴性）。 物理特性与结构 C1q 是由 18 条多肽链组成的高分子量复合物。C1q 的六个臂中，每个臂都包含三条链，分别是 A 链（分子量 26,000 道尔顿）、B 链（分子量 25,000 道尔顿）和 C 链（分子量 24,000 道尔顿）。这三条链约有一半长度相互缠绕，形成类胶原三螺旋结构。该类胶原区域的一半部分构成中心核心，18 条链在此处汇聚。在中心核心区域，各条链通过二硫键以 A - B 和 C - C 的模式连接。类胶原区域的中央存在一个弯曲结构，使得各个臂能够彼此向外伸展。类胶原臂的远端存在球形头部，这些头部具有与免疫球蛋白 Fc 结构域结合的结合位点。C1 复合物由 1 个 C1q 分子（分子量 410,000 道尔顿）、2 个 C1r 分子（每个分子量 92,000 道尔顿）和 2 个 C1s 分子（每个分子量 86,000 道尔顿）组成。在有钙离子存在的情况下，该复合物保持稳定；若去除钙离子，则极易解离。当 C1 被激活时，C1r 和 C1s 亚基会因蛋白水解激活而各自切割成两条链的分子，因此 C1 的 SDS 凝胶图谱极为复杂。 功能 C1q 的生物学功能已在上述 “概述” 和 “物理特性与结构” 部分进行了阐述。可利用 C1q 缺陷血清和 EA 细胞（抗体致敏绵羊红细胞）对 C1q 的功能活性进行检测。这类检测对 C1q 的灵敏度极高，在检测 EA 细胞裂解率的实验中，通常仅需不到 2ng 的 C1q 就能使细胞裂解率达到 50%。 检测方法 补体经典激活途径活性的单位为 CH50（50% 补体溶血单位）。与之类似，C1qH50 则用于定量测定 C1q 的活性。一个 C1qH50 单位的定义为：在总体积为 500μL 的体系中，将一定量的 C1q 与 5 - 20μL 的 C1q 缺陷血清（C1q - Dpl）在 GVB++ 缓冲液（含葡萄糖、明胶、Veronal 缓冲液及钙离子、镁离子的缓冲液）中混合，于 37℃下孵育 30 分钟，能够使 3×10^7 个 EA 细胞（抗体致敏绵羊红细胞）裂解 50% 所需的功能性 C1q 的量。该 C1q 用量体现了检测方法对 C1q 的灵敏度，通常情况下，加入 10μL C1q 缺陷血清时，检测灵敏度约为 1ng C1q。具体批次的数值请参见分析报告。 应用领域 在临床检测中，C1q 可用于包被酶联免疫吸附测定（ELISA）板，进而捕获并定量检测临床样本中的免疫复合物。目前已有多家商业公司销售用于检测和定量免疫复合物的诊断试剂盒，这些试剂盒的设计原理基于 C1q 能够与免疫复合物良好结合，而与单体免疫球蛋白结合能力极弱的特性。 遗传学信息 C1q 各链的 EMBL/Genbank 数据库 cDNA 登录号如下：A 链（P02745）、B 链（P02746）、C 链（P02747）。C1q 的 A、B、C 三条链对应的基因均位于 1 号染色体短臂（1p）上，基因排列顺序为 A - C - B。 缺陷相关病症 目前已发现 C1 的三种组成成分均可能出现缺陷。缺乏 C1q 的患者通常会患有免疫复合物介导的肾脏疾病和皮肤损伤。与所有缺乏补体经典激活途径早期成分的患者一样，C1q 缺陷患者易患系统性红斑狼疮（SLE），且常反复发生化脓性感染。这类患者缺乏补体经典激活途径的功能，其血液中可能检测到 C1q 抗原，也可能检测不到。 相关疾病 详见上述 “缺陷相关病症” 部分。 注意事项 / 毒性 / 危害 该蛋白质从人血清中纯化获得，因此，即便来源血清已通过认证检测证实乙肝表面抗原（HBsAg）、人类 T 淋巴细胞白血病病毒 Ⅰ/Ⅱ 型（HTLV - Ⅰ/Ⅱ）、梅毒血清学试验（STS）均呈阴性，且抗丙型肝炎病毒（HCV）抗体、抗人类免疫缺陷病毒 Ⅰ 型（HIV - 1）抗体及抗人类免疫缺陷病毒 Ⅱ 型（HIV - Ⅱ）抗体也均为阴性，在操作时仍需采取适用于处理所有血液衍生产品的防护措施。 C1q separated from C1r and C1s and from other stabilizing proteins tends to aggregate easily. Because it was isolated and studied in numerous research laboratories, many buffers have been used to stabilize concentrated C1q and prevent aggregation. About half of the scientists prefer high salt and the other prefer 40% glycerol in the storage buffer. C1q is purified from pooled normal human plasma. C1q is part of the C1 complex and this complex is the first complement component in the cascade referred to as the classical pathway of complement. C1 is actually a non-covalent assembly of three different proteins (C1q, C1r, and C1s) bound together in a calcium-dependent complex. C1q has six extended arms with domains at the end of each arm that bind to the Fc domains of immunoglobulins. When antibodies bind to antigens forming immune complexes they cluster allowing two or more of its six arms of C1q to bind to the Fc domains of antibodies such as IgG or IgM. The binding of multiple arms to immune complexes causes the two C1r proteins in the complex (protease zymogens) to auto-activate producing two C1r proteases that cleave and activate the two C1s protease zymogens in the complex. Activated C1s cleaves complement component C4 releasing C4a and initiating covalent attachment of C4b to the activating surface. Activated C1s also cleaves C2 and the larger fragment of C2 binds to the surface-attached C4b forming C4b,C2a which is the C3/C5 convertase of the classical pathway. Extinction Coeff.A ₂₈₀ nm = 0.68 at 1.0 mg/ml for pure C1q Molecular weight:410,000 Da (18 chains) Preservative:None, 0.22 μm filtered. Source:Normal human serum (shown by certified tests to be negative for HBsAg, HTLV-I/II, STS, and for antibodies to HCV, HIV-1 and HIV-II). Physical Characteristics & Structure C1q is a high molecular weight complex of 18 polypeptide chains. Each of the six arms of C1q contains three chains, an A chain (26,000 daltons), a B chain (25,000 daltons) and a C chain (24,000 daltons). The three chains are coiled into a collagen-like triple helix over approximately half their length. Half of this collagen region forms a central core where all 18 chains come together. The chains are joined in this core by disulfides in the pattern A-B and C-C. There is a bend in the center of the collagen region allowing the arms to extend away from each other. Globular heads at the far ends of the collagen arms possess binding sites for Fc domains of immunoglobulins. C1 complex is composed of one C1q molecule (410,000 daltons), two C1r molecules (92,000 daltons) and two C1s molecules (86,000 daltons). The complex is stable in the presence of calcium, but easily dissociates if calcium is removed. When C1 is activated the C1r and C1s subunits are each cleaved into two chain molecules due to proteolytic activation. Thus, the SDS gel pattern of C1 is very complex. Function The biological functions of C1q are described above in the General Description and Physical Characteristics sections. C1q functional activity may be assayed using C1q-depleted serum and EA cells. These assays are extremely sensitive to C1q typically yielding 50% lysis with less than 2 ng C1q in assays measuring the lysis of EA cells. Assays The unit of classical pathway activity is the CH50. A similar unit, the C1qH50, is used to quantitate the activity of C1q. A C1qH50 unit is the amount of functional C1q needed to lyse 50% of 3×10^7 EA cells (antibody-sensitized sheep erythrocytes) when that amount of C1q is incubated with 5-20 μL of C1q-Dpl in GVB++ in a total volume of 500 μL for 30 min at 37℃. This amount of C1q indicates the sensitivity of the assay for C1q which is typically about 1 ng C1q with 10 μL C1q-Dpl. See the Certificate of Analysis for lot specific values. Applications C1q is used to coat ELISA plates to capture and quantitate immune complexes in clinical samples. A number of commercial companies sell diagnostic kits for immune complex detection and quantitation. These kits are based on the ability of C1q to bind well to immune complexes, but to not bind significantly to monomeric immunoglobulins. GeneticsThe EMBL/Genbank cDNA accession numbers are: C1q A chain (P02745), C1q B chain (P02746), and C1q C chain (P02747). The genes for C1q chains A, B and C are all located on chromosome 1p in the order A-C-B. Deficiencies Deficiencies of each of the three components of C1 have been found. Patients lacking C1q generally have immune-complex-mediated renal disease and skin lesions. Like all patients lacking early classical pathway components C1q deficient individuals are prone to systemic lupus erythrematosis (SLE) and recurrent pyogenic infections. They lack classical pathway function and may or may not exhibit C1q antigen in blood. Diseases See section titled Deficiencies above. Precautions/Toxicity/Hazards This protein is purified from human serum and therefore precautions appropriate for handling any blood-derived product must be used even though the source was shown by certified tests to be negative for HBsAg, HTLV-I/II, STS, and for antibodies to HCV, HIV-1 and HIV-II.

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