Nilson B H, Solomon A, Björck L, Akerström B
Department of Medical and Physiological Chemistry, University of Lund, Sweden.
J Biol Chem. 1992 Feb 5;267(4):2234-9.
Protein L is an immunoglobulin light chain-binding protein expressed by some strains of the anaerobic bacterial species Peptostreptococcus magnus. The major variable region subgroups of human kappa and lambda light chains were tested for protein L binding; V kappa I, V kappa III, and V kappa IV bound protein L, whereas no binding occurred with proteins of the V kappa II subgroup or with any lambda light chain subgroups. Studies of the protein L binding capacity of naturally occurring VL fragments, and VL- and CL-related trypsin- and pepsin-derived peptides prepared from a kappa I light chain, localized the site of interaction to the VL domain. The affinity constant for the binding to an isolated V kappa I fragment was comparable to that for the native protein (Ka 0.9 x 10(9) M-1 and Ka 1.5 x 10(9) M-1, respectively). No binding occurred with CL-related fragments. Extensive reduction and alkylation of the V kappa fragment or the native kappa chain resulted in complete loss of protein L binding. Although it is possible, from comparative amino acid sequence data, to identify certain VL-framework region residues that account for the selective binding of protein L by kappa I, kappa III, and kappa IV proteins, our studies indicate that this interaction is essentially dependent upon the tertiary structural integrity of the kappa chain VL domain.
蛋白L是一种由某些厌氧细菌大消化链球菌菌株表达的免疫球蛋白轻链结合蛋白。对人κ和λ轻链的主要可变区亚组进行了蛋白L结合测试；VκI、VκIII和VκIV与蛋白L结合，而VκII亚组的蛋白或任何λ轻链亚组均未发生结合。对天然存在的VL片段以及从κI轻链制备的与VL和CL相关的胰蛋白酶和胃蛋白酶衍生肽的蛋白L结合能力进行的研究，将相互作用位点定位到VL结构域。与分离的VκI片段结合的亲和常数与天然蛋白相当（分别为Ka 0.9×10⁹ M⁻¹和Ka 1.5×10⁹ M⁻¹）。与CL相关的片段未发生结合。Vκ片段或天然κ链的广泛还原和烷基化导致蛋白L结合完全丧失。尽管从比较氨基酸序列数据中有可能识别出某些VL框架区残基，这些残基解释了κI、κIII和κIV蛋白对蛋白L的选择性结合，但我们的研究表明，这种相互作用基本上取决于κ链VL结构域的三级结构完整性。
