The Signal Transduction Mechanisms of a GPI-anchored Complement Regulatory Protein, CD59.

许多蛋白质通过糖基磷脂酰锚点而不是跨膜锚点附着在细胞膜上，并且与细胞内部没有直接接触。尽管如此，gpi锚定蛋白与抗体的交联会引起T细胞和中性粒细胞的激活。活化可能是通过Src激酶介导的。有人认为，gpi锚定分子与激酶的相互作用需要一个跨膜转导元件，其身份仍然存在争议。在本研究中，我们以gpi锚定的补体调节蛋白CD59为模型，阐明gpi锚定蛋白介导信号传导。我们用化学交联剂将表面蛋白交联，然后用抗CD59抗体进行Western blotting，鉴定出CD59相关蛋白。cd59相关分子的大小估计为13-18 kDa。交联产物的双向电泳显示除CD59外没有其他分子的痕迹。交联产物的n端序列与CD59相同，氨基酸组成与CD59惊人地相似。因此，交联产物很可能是CD59二聚体。定位于外膜的CD59都以二聚体的形式存在，这一发现提示了二聚体对CD59功能的重要性。

Many proteins are attached to the cell membranes via glycosyl phosphatidyl anchor rather than by a transmembrane anchor and have no direct contact with the inside of the cells. Despite this, cross-linking of GPI-anchored proteins with antibodies causes activation of T cells and neutrophils. The activation is likely to be mediated through Src kinases. It has been suggested that interaction of the GPI-anchored molecule with kinases requires a transmembrane-transducing element, the identity of which remained controversial.In this study, we focused on a GPI-anchored complement regulatory protein, CD59, as a model, to elucidate the GPI-anchored protein mediating signaling. We identified CD59 associating protein by cross-linking of surface proteins with chemical cross-linker followed by Western blotting with anti-CD59 antibody. The Cd59-associating molecules were estimated to be 13-18 kDa in size. Two-dimensional electrophoresis of the cross-linked products revealed no trace of molecules other than CD59. The cross-linked products showed the same N-terminal sequences as CD59 and a strikingly similar amino acid composition to that of CD59. Thus, most likely, the cross-linked products are CD59 dimers. The finding that CD59 localized on outer membranes is all in the form of dimers suggests the importance of dimerization for CD59 functioning.