Chen Zhe, Singer William D, Danesh Shahab M, Sternweis Paul C, Sprang Stephen R
Department of Pharmacology, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Structure. 2008 Oct 8;16(10):1532-43. doi: 10.1016/j.str.2008.07.009.
G12 class heterotrimeric G proteins stimulate RhoA activation by RGS-RhoGEFs. However, p115RhoGEF is a GTPase Activating Protein (GAP) toward Galpha13, whereas PDZRhoGEF is not. We have characterized the interaction between the PDZRhoGEF rgRGS domain (PRG-rgRGS) and the alpha subunit of G13 and have determined crystal structures of their complexes in both the inactive state bound to GDP and the active states bound to GDPAlF (transition state) and GTPgammaS (Michaelis complex). PRG-rgRGS interacts extensively with the helical domain and the effector-binding sites on Galpha13 through contacts that are largely conserved in all three nucleotide-bound states, although PRG-rgRGS has highest affinity to the Michaelis complex. An acidic motif in the N terminus of PRG-rgRGS occupies the GAP binding site of Galpha13 and is flexible in the GDPAlF complex but well ordered in the GTPgammaS complex. Replacement of key residues in this motif with their counterparts in p115RhoGEF confers GAP activity.
G12类异源三聚体G蛋白通过RGS-RhoGEF刺激RhoA激活。然而，p115RhoGEF是针对Gα13的GTP酶激活蛋白（GAP），而PDZRhoGEF则不是。我们已经对PDZRhoGEF rgRGS结构域（PRG-rgRGS）与G13的α亚基之间的相互作用进行了表征，并确定了它们在与GDP结合的非活性状态以及与GDPAlF（过渡态）和GTPγS（米氏复合物）结合的活性状态下复合物的晶体结构。PRG-rgRGS通过在所有三种核苷酸结合状态下基本保守的接触与Gα13上的螺旋结构域和效应器结合位点广泛相互作用，尽管PRG-rgRGS对米氏复合物具有最高亲和力。PRG-rgRGS N端的一个酸性基序占据Gα13的GAP结合位点，并在GDPAlF复合物中具有灵活性，但在GTPγS复合物中排列有序。用p115RhoGEF中的对应残基替换该基序中的关键残基可赋予GAP活性。
