Viriyakosol S, Mathison J C, Tobias P S, Kirkland T N
Department of Pathology, University of California San Diego School of Medicine, the Veterans Affairs San Diego Healthcare System, San Diego, California 92161, USA.
J Biol Chem. 2000 Feb 4;275(5):3144-9. doi: 10.1074/jbc.275.5.3144.
CD14 is a glycophosphatidylinositol-linked protein expressed by myeloid cells and also circulates as a plasma protein lacking the glycophosphatidylinositol anchor. Both membrane and soluble CD14 function to enhance activation of cells by lipopolysaccharide (LPS), which we refer to as receptor function. We have previously reported the LPS binding and cell activation functions of a group of five deletion mutants of CD14 (Viriyakosol, S., and Kirkland, T.N. (1995) J. Biol. Chem. 270, 361-368). We have now studied the functional impact of these mutations on soluble CD14. We found that some deletions that abrogated LPS binding in membrane CD14 have no effect on LPS binding in soluble CD14. In fact, some of the soluble CD14 deletion mutants bound LPS with an apparent higher affinity than wild-type CD14. Furthermore, we found that all five deletions essentially ablated soluble CD14 LPS receptor function, whereas only two of the deletions completely destroyed membrane CD14 LPS receptor function. Some of the mutants were able to compete with wild-type CD14 in soluble CD14-dependent assays of cellular activation. We concluded that the soluble and membrane forms of CD14 have different structural determinants for LPS receptor function.
CD14是一种由髓样细胞表达的糖磷脂酰肌醇连接蛋白，也以缺乏糖磷脂酰肌醇锚定的血浆蛋白形式循环。膜结合型和可溶性CD14均具有增强脂多糖（LPS）对细胞激活作用的功能，我们将此称为受体功能。我们之前报道过一组五个CD14缺失突变体的LPS结合及细胞激活功能（Viriyakosol, S., and Kirkland, T.N. (1995) J. Biol. Chem. 270, 361 - 368）。我们现在研究了这些突变对可溶性CD14的功能影响。我们发现，一些在膜结合型CD14中消除LPS结合能力的缺失突变，对可溶性CD14的LPS结合能力没有影响。事实上，一些可溶性CD14缺失突变体与LPS结合的亲和力明显高于野生型CD14。此外，我们发现所有五个缺失突变基本上消除了可溶性CD14的LPS受体功能，而只有两个缺失突变完全破坏了膜结合型CD14的LPS受体功能。在可溶性CD14依赖的细胞激活实验中，一些突变体能够与野生型CD14竞争。我们得出结论，CD14的可溶性形式和膜结合形式在LPS受体功能方面具有不同的结构决定因素。
