细胞凋亡的分子生物学-本科-2课件.ppt

7.ICE/Caspases 基因 产物是白介素-1β转化酶,半胱氨酸天冬氨酸特异性蛋白酶,半胱天冬酶,脱冬酶,是一种底物特异的半胱氨酸蛋白酶,已有14个成员. 细胞内ICE蛋白→→→Dnase-actin复合物活化→破坏DNA,诱导细胞凋亡. Figure 1. Schematic illustration of caspase activation and FLICA binding. Caspases are present in nonapoptotic cells as zymogens containing Nterminal prodomain attached to a large (?20 kD) catalytic subunit, which in turn is attached to a small (?10 kD) subunit (A). After induction of apoptosis the procaspases are first cleaved at AspX bonds between the large and small subunits (B). The second cleavage takes place also at Asp site and leads to separation of the prodomain (C). The subunits from two procaspase molecules then assemble into a heterotetramer to form the active enzyme that has two active centers at opposite ends (D). The active enzymatic centers are accessible to the substrates and also can bind FLICA (E). The covalent binding of FLICA is mediated by the halogen (fluoro or chloro) methyl ketone (fmk) moiety which interacts with the cysteine of the active center forming a thiomethyl ketone thereby irreversibly inactivating the enzyme.25,26,30 The specificity of FLICA binding is provided by the sequence of four amino acids in the peptide moiety (e.g., VEID). It should be noted, however, that the threeaminoacid moiety VAD shows no specificity and is a pancaspase inhibitor. The fluorescent tag (carboxyfluorescein, Fam) is located on the other end of FLICA molecule. Figure 2. The pathways to death. Apoptosis can be induced by death receptor signalling and DISC formation or via the activation of the intrinsic apoptotic program. The Bcl-2 family members form the backbone of the intrinsic apoptotic pathway. Growth factor deprivation, glucocorticoids and DNA damage activate pro-apoptotic Bcl-2 family members (via p53 in the cases of DNA damage, via glucocorticoid receptors in the case of glucocorticoids and via other signalling proteins in the case of cytokine withdrawal). The pro-apoptotic members antagonize pro-surviv