Lancaster C A, Taylor-Harris P M, Self A J, Brill S, van Erp H E, Hall A
Chester Beatty Laboratories, Institute of Cancer Research, London, United Kingdom.
J Biol Chem. 1994 Jan 14;269(2):1137-42.
GTPase-activating proteins or GAPs play an important role in signal transduction pathways regulated by GTP-binding proteins. In addition to acting as down-regulators of GTPases, there is growing evidence that they also act as effector molecules required for downstream signaling. PLC-beta 1, the target protein regulated by the heterotrimeric GTPase Gq, has been shown to be a GAP, whereas rasGAP, a down-regulator of the small GTPase ras, may be required for the ras-mediated signals. We have purified a GAP specific for the rho subfamily of small GTPases. Partial sequence analysis of rhoGAP has led to the identification of a family of related proteins which now includes bcr, chimaerin, p190, p85, and 3BP-1. We report here the isolation of a cDNA clone encoding human rhoGAP and the expression of recombinant protein. The full-length protein is 50 kDa and is ubiquitously expressed in mammalian cells. At least three members of the rho family are substrates for rhoGAP, rho, rac, and G25K/CDC42, and they each bind equally well to the protein. In vitro GTPase assays, however, reveal that G25K/CDC42 is the preferred substrate. RhoGAP contains a proline-rich sequence, suggesting that it is an SH3-binding protein.
GTP酶激活蛋白（GAPs）在由GTP结合蛋白调节的信号转导途径中发挥重要作用。除了作为GTP酶的负调节因子外，越来越多的证据表明它们还作为下游信号传导所需的效应分子发挥作用。PLC-β1是由异三聚体GTP酶Gq调节的靶蛋白，已被证明是一种GAP，而小GTP酶ras的负调节因子rasGAP可能是ras介导的信号所必需的。我们纯化了一种对小GTP酶的rho亚家族具有特异性的GAP。对rhoGAP的部分序列分析导致鉴定出一个相关蛋白家族，现在该家族包括bcr、嵌合体蛋白、p190、p85和3BP-1。我们在此报告编码人rhoGAP的cDNA克隆的分离及重组蛋白的表达。全长蛋白为50 kDa，在哺乳动物细胞中普遍表达。rho家族的至少三个成员是rhoGAP的底物，即rho、rac和G25K/CDC42，它们与该蛋白的结合能力相当。然而，体外GTP酶分析表明，G25K/CDC42是首选底物。RhoGAP包含一个富含脯氨酸的序列，表明它是一种SH3结合蛋白。
