蛋白激酶Cα相互作用蛋白1(protein interacting with Cαkinase 1,PICK1)是衔接膜上受体和蛋白激酶Cα的重要蛋白.利用荧光光谱结合定点突变技术、蛋白与脂质覆盖法等方法,分析了PICK1蛋白N末端区域几个酸性氨基酸残基对PDZ结构域与膜脂结合的影响,以及钙离子结合N末端酸性区域对PDZ脂结合能力的调节.结果显示,带有上游酸性区域的PDZ结构域(NPDZ)的脂质结合能力仅相当PDZ结构域的15%,相比单独的PDZ结构域与脂质的解离常数Kd(PDZ)为1.58×103μg.L-1,NPDZ与脂质解离常数Kd(NPDZ)为3.3×104μg.L-1,其中在N末端酸性残基中D8与D12两个天冬氨酸是影响脂质结合能力减弱的关键残基,若将二者分别突变为丙氨酸后,NPDZ与脂质的解离常数分别为:Kd(D8/A)=4.42×103μg.L-1;Kd(D12/A)=1.73×103μg.L-1接近于PDZ结构域与脂质结合能力;钙离子会增强NPDZ脂结合能力,当钙离子浓度达到30μmol/L时,NPDZ的脂结合能力提高2.3倍,但只相当于PDZ的50%的结合能力.
Two DNA fragments encoding PDZ domain(21-110 residues) and BAR domain(150-360 residues) from PICK1(1-416 residues) were amplified by PCR and then introduced into vectors, pET-32M and pMAL-c2X respectively to generate recombinant plasmids, pE-pdz and pM-bar. Having been separately transferred into the hosts E.coli BL21 and E.coli JM109, these two strains can express fusion proteins: His-tagged PDZ(PDZ domain) and maltose binding protein-BAR(MBP-BAR domain) respectively, as confirmed by both SDS-PAGE and Western blotting. The interaction between these two domains is dose-dependence, as identified by a pull-down test. Moreover, it has been shown from the ELISA analysis that the actual amount of PDZ bound to MBP-BAR-amylose beads reaches (16±0.5)%, as calculated by the molar ratio of PDZ to MBP-BAR. In addition, the interaction between BAR(bait) and PDZ(prey) in vivo was also examined with a yeast two-hybrid system.
