Gay N J, Ntwasa M
Department of Biochemistry, University of Cambridge, UK.
FEBS Lett. 1993 Dec 6;335(2):155-60. doi: 10.1016/0014-5793(93)80720-f.
The cactus protein is the Drosophila homologue of the mammalian I kappa B family of cytoplasmic anchor proteins. We have expressed in E. coli and purified a cactus fusion protein, CACT-Bgl. CACT-Bgl protein contains the six ankyrin repeat sequences which are necessary for specific binding to the Drosophila rel family transcription factor dorsal. We show that the purified CACT-Bgl protein can bind specifically to dorsal and, using circular dichroism spectroscopy, that the protein adopts a largely alpha-helical secondary structure. A further analysis of the ankyrin repeat domains of cactus, using an improved secondary structure prediction program indicates that the N-terminal of the repeat will form into a loop structure and the C-terminal section into an interrupted, amphipathic alpha-helix. On the basis of these findings we propose that the ankyrin repeats of cactus fold together into helical bundles interconnected by diverged loops.
仙人掌蛋白是哺乳动物细胞质锚定蛋白IκB家族在果蝇中的同源物。我们已在大肠杆菌中表达并纯化了一种仙人掌融合蛋白CACT-Bgl。CACT-Bgl蛋白包含六个锚蛋白重复序列，这些序列是与果蝇rel家族转录因子背侧特异性结合所必需的。我们表明，纯化的CACT-Bgl蛋白可以与背侧特异性结合，并且使用圆二色光谱法表明该蛋白主要采用α-螺旋二级结构。使用改进的二级结构预测程序对仙人掌的锚蛋白重复结构域进行的进一步分析表明，重复序列的N端将形成环结构，C端部分形成间断的两亲性α-螺旋。基于这些发现，我们提出仙人掌的锚蛋白重复序列折叠在一起形成由发散环相互连接的螺旋束。
