Mayeenuddin Linnia H, McIntire William E, Garrison James C
Department of Pharmacology, University of Virginia Health System, Charlottesville, VA 22908, USA.
J Biol Chem. 2006 Jan 27;281(4):1913-20. doi: 10.1074/jbc.M506034200. Epub 2005 Nov 21.
P-Rex1 is a specific guanine nucleotide exchange factor (GEF) for Rac, which is present in high abundance in brain and hematopoietic cells. P-Rex1 is dually regulated by phosphatidylinositol (3,4,5)-trisphosphate and the Gbetagamma subunits of heterotrimeric G proteins. We examined which of the multiple G protein alpha and betagamma subunits activate P-Rex1-mediated Rac guanine nucleotide exchange using pure, recombinant proteins reconstituted into synthetic lipid vesicles. AlF(-)(4) activated G(s),G(i),G(q),G(12), or G(13) alpha subunits were unable to activate P-Rex1. Gbetagamma dimers containing Gbeta(1-4) complexed with gamma(2) stimulated P-Rex1 activity with EC(50) values ranging from 10 to 20 nm. Gbeta(5)gamma(2) was not able to stimulate P-Rex1 GEF activity. Dimers containing the beta(1) subunit complexed with a panel of different Ggamma subunits varied in their ability to stimulate P-Rex1. The beta(1)gamma(3), beta(1)gamma(7), beta(1)gamma(10), and beta(1)gamma(13HA) dimers all activated P-Rex1 with EC(50) values ranging from 20 to 38 nm. Dimers composed of beta(1)gamma(12) had lower EC(50) values (approximately 112 nm). The farnesylated gamma(11) subunit is highly expressed in hematopoietic cells; surprisingly, dimers containing this subunit (beta(1)gamma(11)) were also less effective at activating P-Rex1. These findings suggest that the composition of the Gbetagamma dimer released by receptor activation may differentially activate P-Rex1.
P-Rex1是一种针对Rac的特异性鸟嘌呤核苷酸交换因子（GEF），在脑和造血细胞中大量存在。P-Rex1受磷脂酰肌醇（3,4,5）-三磷酸和异源三聚体G蛋白的Gβγ亚基双重调节。我们使用重组到合成脂质囊泡中的纯重组蛋白，研究了多个G蛋白α和βγ亚基中哪些能激活P-Rex1介导的Rac鸟嘌呤核苷酸交换。AlF(-)(4)激活的G(s)、G(i)、G(q)、G(12)或G(13)α亚基均无法激活P-Rex1。含有与γ(2)复合的Gβ(1-4)的Gβγ二聚体刺激P-Rex1活性，其半数有效浓度（EC(50)）值在10至20纳米范围内。Gβ(5)γ(2)无法刺激P-Rex1的GEF活性。含有β(1)亚基并与一组不同Gγ亚基复合的二聚体，在刺激P-Rex1的能力上存在差异。β(1)γ(3)、β(1)γ(7)、β(1)γ(10)和β(1)γ(13HA)二聚体均能激活P-Rex1，EC(50)值在20至38纳米范围内。由β(1)γ(12)组成的二聚体EC(50)值较低（约112纳米）。法尼基化的γ(11)亚基在造血细胞中高度表达；令人惊讶的是，含有该亚基的二聚体（β(1)γ(11)）在激活P-Rex1方面也效果较差。这些发现表明，受体激活释放的Gβγ二聚体的组成可能会以不同方式激活P-Rex1。
