Kihlberg B M, Sjöholm A G, Björck L, Sjöbring U
Department of Cell and Molecular Biology, Section for Molecular Pathogenesis, Lund University, Sweden.
Eur J Biochem. 1996 Sep 15;240(3):556-63. doi: 10.1111/j.1432-1033.1996.0556h.x.
Protein LG is a 50-kDa hybrid molecule containing four Ig-light-chain-binding domains from protein L of Peptostreptococcus magnus and two IgG-Fe-binding repeats from streptococcal protein G. Here we analyse the binding of protein LG to Ig from several mammalian species. Protein LG was shown to bind human IgG of all subclasses and other Ig classes that carry kappa chains. The binding to human IgG was only marginally influenced by changes in temperature (4-37 degrees C) or salt concentration (0-1.6 M), and was stable over a wide pH range (pH 4-10). Protein LG bound to Ig from 11 of 12 mammalian species, including those of rabbit, mouse and rat. The affinity constants obtained for the interactions between protein LG and polyclonal IgG from rabbit (4.0 x 10(9) M-1), mouse (1.7 x 10(9) M-1) and rat (1.3 x 10(9) M-1) were similar to the value previously reported for the interaction between the hybrid protein and human polyclonal IgG (5.9 x 10(9) M-1). The interaction between protein LG and a mouse IgG mAb was not influenced by the presence of the specific protein antigen, nor was the binding of this antibody to its ligand affected by protein LG. Inhibition experiments demonstrated that the Ig-binding site of one of the fusion partners retained its ligand-binding capacity when the other component was occupied. Protein LG selectively absorbed 85-90% of the total Ig present in human and rabbit sera and 75-80% of the Ig in sera from mouse and rat. Human serum depleted of C1q, factor D and properdin and preabsorbed by protein LG could be used as a source for other complement factors. These data demonstrate that protein LG is a very versatile Ig-binding protein.
蛋白LG是一种50 kDa的杂合分子，包含来自大消化链球菌蛋白L的四个Ig轻链结合结构域和来自链球菌蛋白G的两个IgG-Fe结合重复序列。在此，我们分析了蛋白LG与几种哺乳动物物种的Ig的结合情况。结果表明，蛋白LG能结合所有亚类的人IgG以及其他携带κ链的Ig类别。其与人IgG的结合仅受到温度（4 - 37℃）或盐浓度（0 - 1.6 M）变化的轻微影响，并且在较宽的pH范围（pH 4 - 10）内保持稳定。蛋白LG能与12种哺乳动物中的11种的Ig结合，包括兔、小鼠和大鼠。蛋白LG与兔多克隆IgG（4.0×10⁹ M⁻¹）、小鼠多克隆IgG（1.7×10⁹ M⁻¹）和大鼠多克隆IgG（1.3×10⁹ M⁻¹）相互作用获得的亲和常数，与先前报道的该杂合蛋白与人多克隆IgG相互作用的值（5.9×10⁹ M⁻¹）相似。蛋白LG与小鼠IgG单克隆抗体之间的相互作用不受特定蛋白抗原存在的影响，该抗体与其配体的结合也不受蛋白LG的影响。抑制实验表明，当一个融合伙伴的其他成分被占据时，其中一个融合伙伴的Ig结合位点仍保留其配体结合能力。蛋白LG能选择性地吸附人血清和兔血清中85 - 90%的总Ig，以及小鼠和大鼠血清中75 - 80%的Ig。去除C1q、因子D和备解素并经蛋白LG预吸附的人血清可作为其他补体因子的来源。这些数据表明蛋白LG是一种非常通用的Ig结合蛋白。
