Jonsson H, Lindmark H, Guss B
Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala.
Infect Immun. 1995 Aug;63(8):2968-75. doi: 10.1128/iai.63.8.2968-2975.1995.
This work describes the cloning and sequencing of a gene encoding a plasma protein receptor from Streptococcus zooepidemicus. This receptor, termed protein ZAG, is a 45-kDa protein that binds alpha 2-macroglobulin (alpha 2M), serum albumin, and immunoglobulin G (IgG). The IgG-binding activity is located in the C-terminal part of the molecule and is mediated by two repeated domains highly homologous to each other as well as to the corresponding domains in streptococcal type III Fc receptors. The IgG-binding profile of protein ZAG is similar to that previously reported for S. zooepidemicus. Binding to serum albumin is mediated by a short amino acid sequence in the middle of the molecule. This domain shows homology to previously described albumin-binding proteins from streptococci, and the albumin-binding profile of protein ZAG is similar to that of streptococcal protein G. The N-terminal part of protein ZAG, which mediates binding to the plasma proteinase inhibitor alpha 2M, is composed of a unique stretch of amino acids. Protein ZAG competes for the same, or nearby, binding site(s) in alpha 2M as do two recently described Streptococcus dysgalactiae receptors, although the sequences of the alpha 2M-binding domains in these three receptors show only minor sequence similarities.
这项研究描述了兽疫链球菌血浆蛋白受体编码基因的克隆与测序。这种受体被称为蛋白ZAG，是一种45 kDa的蛋白，可结合α2-巨球蛋白（α2M）、血清白蛋白和免疫球蛋白G（IgG）。IgG结合活性位于分子的C末端，由两个彼此高度同源且与链球菌III型Fc受体中的相应结构域高度同源的重复结构域介导。蛋白ZAG的IgG结合谱与先前报道的兽疫链球菌相似。与血清白蛋白的结合由分子中部的一段短氨基酸序列介导。该结构域与先前描述的链球菌白蛋白结合蛋白具有同源性，蛋白ZAG的白蛋白结合谱与链球菌蛋白G相似。蛋白ZAG的N末端介导与血浆蛋白酶抑制剂α2M的结合，由一段独特的氨基酸序列组成。尽管这三种受体中α2M结合结构域的序列仅显示出微小的序列相似性，但蛋白ZAG与最近描述的两种停乳链球菌受体竞争α2M中相同或附近的结合位点。
