Nickells M W, Seya T, Holers V M, Atkinson J P
Mol Immunol. 1986 Jun;23(6):661-8. doi: 10.1016/0161-5890(86)90104-5.
The human C3b/C4b receptor (CR1) binds the major activation and opsonic fragments of the third (C3) and fourth (C4) components of complement. CR1 is a single chain integral membrane glycoprotein widely distributed on peripheral blood cells. Four codominantly inherited allelic variants with Mrs of 160,000, 190,000, 220,000 and 250,000 have been described. To address the structural basis for this unusual polymorphism, CR1 from donors expressing three of the four allelic variants was purified from surface labeled (125I) erythrocytes by iC3-Sepharose affinity chromatography and the variants compared by tryptic peptide mapping (TPM). The TPMs of each variant contained the same major peaks and minor peak areas and were nearly identical to one another. Tryptic peptide mappings of the 190,000 Mr erythrocyte CR1, which was purified prior to iodination, were similar to those derived from surface iodinated CR1. The TPMs of erythrocyte and granulocyte CR1 from the same donor differed by a single peak of increased prominence in the granulocyte map. These results indicate a conservation in amino acid sequence for those peptides detected. In view of these data and those of other studies of the structure and genetics of CR1 and related proteins, it is suggested in this paper that the allelic variation relates to CR1, being composed of repeating amino acid sequences.
人C3b/C4b受体（CR1）可结合补体第三成分（C3）和第四成分（C4）的主要激活片段及调理素片段。CR1是一种单链整合膜糖蛋白，广泛分布于外周血细胞。已描述了四种共显性遗传的等位基因变体，其分子量分别为160,000、190,000、220,000和250,000。为探究这种异常多态性的结构基础，通过iC3 - 琼脂糖亲和层析从表面标记（125I）红细胞中纯化了表达四种等位基因变体中三种的供体的CR1，并通过胰蛋白酶肽图谱分析（TPM）比较这些变体。每个变体的TPM包含相同的主要峰和次要峰区域，且彼此几乎相同。碘化前纯化的190,000分子量红细胞CR1的胰蛋白酶肽图谱与表面碘化CR1的图谱相似。来自同一供体的红细胞和粒细胞CR1的TPM仅在粒细胞图谱中有一个突出增加的单峰不同。这些结果表明所检测到的那些肽的氨基酸序列具有保守性。鉴于这些数据以及其他关于CR1和相关蛋白结构与遗传学的研究数据，本文提出等位基因变异与由重复氨基酸序列组成的CR1相关。
