STRUCTURES OF ACTIVE CONFORMATIONS OF G(I-ALPHA-1) AND THE MECHANISM OF GTP HYDROLYSIS
STRUCTURES OF ACTIVE CONFORMATIONS OF G(I-ALPHA-1) AND THE MECHANISM OF GTP HYDROLYSIS
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DOI：
10.1126/science.8073283
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发表时间：
1994-09-02
期刊：
影响因子：
56.9
通讯作者：
SPRANG, SR
中科院分区：
文献类型：
--
作者：
COLEMAN, DE;BERGHUIS, AM;SPRANG, SR
G蛋白α亚单位-p21(Ras)超家族成员对三磷酸鸟苷(GTP)的水解机制已被广泛研究，但还不是很清楚。由G蛋白G(Iα1)形成的GTP-S和GDP-AlF4-络合物的高分辨X射线结构表明，在两个高度保守的残基的过渡态稳定中发挥了特殊的作用。谷氨酰胺(204)(p21(Ras)中的谷氨酰胺(61))稳定和定向了处于三角-双锥过渡状态的水解水。精氨酸178稳定五配位磷酸盐中间体赤道氧原子上的负电荷。该残基仅在G(α)家族中保守，这可能是G(α)蛋白的水解率高于p21(Ras)家族成员的原因。G(iα1)的折叠不同于同源G(tα)亚基的折叠，这是位于这些蛋白质特有的α-螺旋结构域上的螺旋环序列的构象；该位置可能参与了效应器的结合。在GTPγS-G(Iα1)中，氨基末端33个残基是无序的，这表明当GTP激活α亚基时，可能有促进βγ亚基复合体释放的机制。
Mechanisms of guanosine triphosphate (GTP) hydrolysis by members of the G protein alpha subunit-p21(ras) superfamily of guanosine triphosphatases have been studied extensively but have not been well understood. High-resolution x-ray structures of the GTP gamma S and GDP.AlF4- complexes formed by the G protein G(i alpha 1) demonstrate specific roles in transition-state stabilization for two highly conserved residues. Glutamine(204)(Gln(61) in p21(ras)) stabilizes and orients the hydrolytic water in the trigonal-bipyramidal transition state. Arginine 178 stabilizes the negative charge at the equatorial oxygen atoms of the pentacoordinate phosphate intermediate. Conserved only in the G(alpha) family, this residue may account for the higher hydrolytic rate of G(alpha) proteins relative to those of the p21(ras) family members. The fold of G(i alpha 1) differs from that of the homologous G(t alpha) subunit in the conformation of a helix-loop sequence located in the alpha-helical domain that is characteristic of these proteins; this site may participate in effector binding. The amino-terminal 33 residues are disordered in GTP gamma S-G(i alpha 1), suggesting a mechanism that may promote release of the beta gamma subunit complex when the a subunit is activated by GTP.