Fujisawa T, Uruga T, Yamaizumi Z, Inoko Y, Nishimura S, Ueki T
Institute of Physical and Chemical Research (RIKEN), Saitama.
J Biochem. 1994 May;115(5):875-80. doi: 10.1093/oxfordjournals.jbchem.a124433.
The small-angle X-ray scattering technique was used to characterize the structure in solution of wild type ras p21 as well as the oncogenic proteins mutated at residue 12, 59, or 61. In the presence of GDP, the radius of gyration, Rg, determined for wild type ras p21 was 16.89 +/- 0.01 A, while the wild type ras p21 bound to the GTP analogue GDPNHP (5'-guanyl imido diphosphate beta-gamma-imidoguanosine 5'-triphosphate) showed an Rg value of 17.46 +/- 0.01 A, which is 3.3% larger. The result shows that ras p21 expands upon GTP binding. The Rgs of mutated proteins were 17.04 +/- 0.01, 16.98 +/- 0.01, and 17.03 +/- 0.01 A for the Gly-12 to Val, Ala-59 to Thr, and Gln-61 to Leu mutants, respectively. The scattering profiles were analyzed by simulation of hydrated ras p21, based on the crystal atomic coordinates, and it was concluded that the ras p21 molecule incorporates 20% more bulk water upon GTP binding. The increase of bulk water is especially conspicuous around the interface between switch I (residues 32-40) and switch II (residues 60-66) regions. This suggests that hydration plays an important role in the interaction with GAP.
小角X射线散射技术被用于表征野生型ras p21以及在第12、59或61位残基处发生突变的致癌蛋白在溶液中的结构。在GDP存在的情况下，野生型ras p21的回转半径Rg为16.89±0.01 Å，而与GTP类似物GDPNHP（5'-鸟苷亚氨二磷酸β-γ-亚氨基鸟苷5'-三磷酸）结合的野生型ras p21的Rg值为17.46±0.01 Å，大3.3%。结果表明，ras p21在结合GTP时会扩张。对于Gly-12突变为Val、Ala-59突变为Thr以及Gln-61突变为Leu的突变蛋白，其Rg值分别为17.04±0.01、16.98±0.01和17.03±0.01 Å。基于晶体原子坐标，通过对水合ras p21的模拟分析散射曲线，得出结论：ras p21分子在结合GTP时结合的大量水增加了20%。在开关I（残基32 - 40）和开关II（残基60 - 66）区域之间的界面周围，大量水的增加尤为明显。这表明水合作用在与GAP的相互作用中起重要作用。
