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P21~(ras)蛋白是 ras 基因家族的 Ha-ras、Ki-ras 和 N-ras 癌基因编码的蛋白质,分子量为21KD.p21蛋白可将表皮生长因子(EGF)和胰岛素的刺激信号传入相应的靶细胞内.EGF 受体和胰岛素受体均可使 p21蛋白磷酸化,并刺激 p21蛋白的 GTP 结合活性.p21蛋白具有 GTP 酶活性,结合和水解 GTP 是调节 p21蛋白活性状态的方式.p21蛋白作用的靶分子很可能是磷酯酶 C,磷酯酶 C 则可水解4,5-二磷酸磷酯酰肌醇,产生三磷酸肌醇和甘油二酯等细胞内第二信使.p21蛋白通过 C-末端的4个氨基酸与类脂结合而定位于细胞膜内表面,只有定位在膜上才能发挥其生物功能。当 ras 基因发生点突变而使 p21蛋白失去结合 GTP 的能力时,p21即失去其生物功能。如果突变发生在 GTP 结合部位,只是影响 p21蛋白水解 GTP 的能力,而不影响其结合 GTP 的能力,则 p21蛋白可持续向细胞内传递信号,导致细胞癌变,这种突变是 ras 癌基因激活的主要方式.
The P21 ras protein is a protein encoded by the Ha-ras, Ki-ras and N-ras oncogenes of the ras gene family and has a molecular weight of 21 kD. The p21 protein can deliver the stimulatory signals of epidermal growth factor (EGF) and insulin Of target cells.EEG receptor and insulin receptor can phosphorylate p21 protein and stimulate the GTP binding activity of p21 protein.p21 protein has GTPase activity, binding and hydrolysis of GTP is a way to regulate the activity of p21 protein.p21 The target of the protein action is likely to be phosphatase C, which hydrolyzes phosphatidyl 4,5-diphosphate to produce a second intracellular messenger such as inositol triphosphate and diglyceride. The p21 protein passes C-terminal 4 amino acids and lipid binding located on the membrane surface, only in the membrane to play its biological function. When the ras gene is mutated and the p21 protein loses the ability to bind GTP, p21 loses its biological function. If the mutation occurs at the GTP binding site and only affects the ability of p21 to hydrolyze GTP without affecting its ability to bind to GTP, the p21 protein can continue to transmit signals to cells resulting in canceration of the cell that is activated by the ras oncogene Main way.