Ramprasad M P, Fischer W, Witztum J L, Sambrano G R, Quehenberger O, Steinberg D
Department of Medicine, University of California, La Jolla 92093, USA.
Proc Natl Acad Sci U S A. 1995 Oct 10;92(21):9580-4. doi: 10.1073/pnas.92.21.9580.
We have previously reported the partial purification of a 94- to 97-kDa plasma membrane protein from mouse peritoneal macrophages that binds oxidatively modified low density lipoprotein (OxLDL) and phosphatidylserine-rich liposomes. We have now identified that protein as macrosialin, a previously cloned macrophage-restricted membrane protein in the lysosomal-associated membrane protein family (mouse homologue of human CD68). Early in the course of purification of the 94- to 97-kDa protein, a new OxLDL-binding band at 190-200 kDa appeared and copurified with the 94- to 97-kDa protein. The HPLC pattern of tryptic peptides from this higher molecular mass ligand-binding band closely matched that derived from the 94- to 97-kDa band. Specifically, the same three macrosialin-derived tryptic peptides (9, 9, and 15 residues) were present in the purified 94- to 97-kDa band and in the 190- to 200-kDa band and antisera raised against peptide sequences in macrosialin recognized both bands. An antiserum against macrosialin precipitated most of the 94- to 97-kDa OxLDL-binding material. We conclude that the binding of OxLDL to mouse macrophage membranes is in part attributable to macrosialin. Our previous studies show that OxLDL competes with oxidized red blood cells and with apoptotic thymocytes for binding to mouse peritoneal macrophages. Whether macrosialin plays a role in recognition of OxLDL and oxidatively damaged cells by intact macrophages remains uncertain.
我们之前报道过从小鼠腹腔巨噬细胞中部分纯化出一种94至97千道尔顿的质膜蛋白，该蛋白能结合氧化修饰的低密度脂蛋白（OxLDL）和富含磷脂酰丝氨酸的脂质体。我们现已鉴定出该蛋白为巨唾液酸蛋白，它是溶酶体相关膜蛋白家族中先前克隆的巨噬细胞限制性膜蛋白（人类CD68的小鼠同源物）。在纯化94至97千道尔顿蛋白的过程中，早期出现了一条190至200千道尔顿的新OxLDL结合带，并与94至97千道尔顿的蛋白共同纯化。来自这个较高分子量配体结合带的胰蛋白酶肽的高效液相色谱图谱与94至97千道尔顿带的图谱紧密匹配。具体而言，纯化的94至97千道尔顿带和190至千道尔顿带中存在相同的三个源自巨唾液酸蛋白的胰蛋白酶肽（9、9和15个残基），针对巨唾液酸蛋白中肽序列产生的抗血清能识别这两条带。针对巨唾液酸蛋白的抗血清沉淀了大部分94至97千道尔顿的OxLDL结合物质。我们得出结论，OxLDL与小鼠巨噬细胞膜的结合部分归因于巨唾液酸蛋白。我们之前的研究表明，OxLDL与氧化红细胞和凋亡胸腺细胞竞争结合小鼠腹腔巨噬细胞。完整巨噬细胞中巨唾液酸蛋白是否在识别OxLDL和氧化损伤细胞中发挥作用仍不确定。
