Cahir McFarland E D, Thomas M L
Howard Hughes Medical Institute, Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Biol Chem. 1995 Nov 24;270(47):28103-7. doi: 10.1074/jbc.270.47.28103.
CD45 is a transmembrane protein-tyrosine phosphatase required for antigen receptor signaling in lymphocytes. CD45 activates the Src family protein-tyrosine kinases, p56lck and p59fyn, by dephosphorylating a negative regulatory tyrosine in the carboxyl terminus. Immunoprecipitation of CD45 precipitates p56lck and CD45AP. Although the function of CD45AP is unknown, it has been proposed to be an adapter between p56lck and CD45. To assess the ability of CD45AP to function as an adapter, we determined the regions required for the interaction with CD45 by expressing chimeric proteins in HeLa cells. CD45AP has a region similar to a potential protein-protein interaction domain, the WW domain. Surprisingly, this domain was not necessary for the association with CD45. Rather, a 40-amino acid sequence encompassing the putative transmembrane domain of CD45AP was sufficient to mediate binding to CD45. Similarly, a 39-amino acid sequence encompassing the CD45 transmembrane region was sufficient to direct the interaction with CD45AP. Expression of p56lck with CD45AP resulted in an interaction that could only be detected by in vitro kinase reaction, suggesting that the association of p56lck and CD45AP is weak. These data support a model in which CD45AP links CD45 with other proteins but not necessarily p56lck.
CD45是淋巴细胞中抗原受体信号传导所需的一种跨膜蛋白酪氨酸磷酸酶。CD45通过使羧基末端的一个负调节酪氨酸去磷酸化来激活Src家族蛋白酪氨酸激酶p56lck和p59fyn。CD45的免疫沉淀会沉淀出p56lck和CD45AP。尽管CD45AP的功能尚不清楚，但有人提出它是p56lck和CD45之间的衔接蛋白。为了评估CD45AP作为衔接蛋白的功能能力，我们通过在HeLa细胞中表达嵌合蛋白来确定与CD45相互作用所需的区域。CD45AP有一个类似于潜在蛋白-蛋白相互作用结构域WW结构域的区域。令人惊讶的是，该结构域对于与CD45的结合并非必需。相反，包含CD45AP假定跨膜结构域的一个40个氨基酸的序列足以介导与CD45的结合。同样，包含CD45跨膜区域的一个39个氨基酸的序列足以指导与CD45AP的相互作用。p56lck与CD45AP的表达导致一种只能通过体外激酶反应检测到的相互作用，这表明p56lck与CD45AP的结合较弱。这些数据支持了一个模型，即CD45AP将CD45与其他蛋白联系起来，但不一定与p56lck联系。
