Akerström B, Brodin T, Reis K, Björck L
J Immunol. 1985 Oct;135(4):2589-92.
Protein G is an immunoglobulin (IgG)-binding bacterial cell wall protein recently isolated from group G streptococci. We have investigated the avidity of protein G for various monoclonal and polyclonal Ig of the IgG class, and compared it with the binding properties of protein A, the staphylococcal Fc-binding protein. Radiolabeled Ig were mixed with Sepharose-coupled protein G or protein A, and the amounts of radioactivity bound to the matrix-coupled bacterial proteins were determined. The avidity was found to be greater for protein G than for protein A for all examined Ig. Protein G bound all tested monoclonal IgG from mouse IgG1, IgG2a, and IgG3, and rat IgG2a, IgG2b, and IgG2c. In addition, polyclonal IgG from man, cow, rabbit, goat, rat, and mouse bound to protein G, whereas chicken IgG did not. The binding property of protein G was additionally exploited in the Western blot assay, in which iodine-labeled protein G was used successfully for the detection of a rat monoclonal antibody against ovalbumin, and for the detection of rabbit and goat polyclonal whole antisera against human urinary proteins. In these experimental situations, protein G was found to be a powerful reagent for the detection of IgG, and consequently the antigen against which these antibodies are directed.
蛋白G是一种最近从G群链球菌中分离出的能结合免疫球蛋白（IgG）的细菌细胞壁蛋白。我们研究了蛋白G对各种IgG类单克隆和多克隆Ig的亲和力，并将其与葡萄球菌Fc结合蛋白A蛋白的结合特性进行了比较。将放射性标记的Ig与琼脂糖偶联的蛋白G或蛋白A混合，然后测定与基质偶联的细菌蛋白结合的放射性量。结果发现，对于所有检测的Ig，蛋白G的亲和力均高于蛋白A。蛋白G能结合来自小鼠IgG1、IgG2a和IgG3以及大鼠IgG2a、IgG2b和IgG2c的所有测试单克隆IgG。此外，人、牛、兔、山羊、大鼠和小鼠的多克隆IgG能与蛋白G结合，而鸡IgG则不能。蛋白G的结合特性还被用于蛋白质印迹分析，其中碘标记的蛋白G成功用于检测抗卵清蛋白的大鼠单克隆抗体，以及检测抗人尿蛋白的兔和山羊多克隆全抗血清。在这些实验中，发现蛋白G是检测IgG以及相应抗原的有力试剂。
