Kitamura K, Maiti A, Ng D H, Johnson P, Maizel A L, Takeda A
Department of Pathology, Roger Williams Medical Center-Brown University, Providence, Rhode Island 02908, USA.
J Biol Chem. 1995 Sep 8;270(36):21151-7. doi: 10.1074/jbc.270.36.21151.
CD45, a leukocyte-specific transmembrane protein tyrosine phosphatase, is required for critical signal transduction pathways in immune responses. To elucidate the molecular interactions of CD45 with other proteins involved in CD45-mediated signal transduction pathways, we have recently cloned a 30-kDa phosphorylated protein, CD45-AP, which specifically associates with CD45. Binding analysis employing several deleted or chimeric forms of CD45-AP and CD45 demonstrated that the potential transmembrane segment of CD45-AP bound to the transmembrane portion of CD45. CD45-AP was found in particulate fractions of lymphocytes along with CD45, indicating that it is likely to be a transmembrane protein. In addition, CD45-AP was resistant to proteolysis by tosylphenylalanyl chloromethyl ketone-treated trypsin applied to intact cells. This is consistent with the most likely membrane orientation of CD45-AP predicted from the amino acid sequence, that is, only a short amino-terminal segment of CD45-AP is extracellular. We propose that CD45-AP interacts with CD45 at the plasma membrane and that the bulk of CD45-AP located in the cytoplasm act as an adapter which directs the interaction between CD45 and other molecules involved in CD45-mediated signal transduction pathways.
CD45是一种白细胞特异性跨膜蛋白酪氨酸磷酸酶，免疫应答中的关键信号转导途径需要该酶的参与。为了阐明CD45与参与CD45介导的信号转导途径的其他蛋白之间的分子相互作用，我们最近克隆了一种30 kDa的磷酸化蛋白CD45-AP，它能特异性地与CD45结合。采用几种缺失或嵌合形式的CD45-AP和CD45进行的结合分析表明，CD45-AP的潜在跨膜片段与CD45的跨膜部分结合。在淋巴细胞的颗粒部分发现了CD45-AP和CD45，这表明它可能是一种跨膜蛋白。此外，将用甲苯磺酰苯丙氨酰氯甲基酮处理的胰蛋白酶应用于完整细胞时，CD45-AP对其蛋白水解具有抗性。这与根据氨基酸序列预测的CD45-AP最可能的膜取向一致，即CD45-AP只有一个短的氨基末端片段位于细胞外。我们提出，CD45-AP在质膜处与CD45相互作用，位于细胞质中的大部分CD45-AP充当衔接子，指导CD45与参与CD45介导的信号转导途径的其他分子之间的相互作用。
