title: The Drosophila ankyrin repeat protein cactus has a predominantly alpha-helical secondary structure.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Cambridge, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Gay
authors.forename: M
authors.initials: M
authors.lastname: Ntwasa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D015252:Deoxyribonucleases, Type II Site-Specific / Q000737:chemistry / Q000235:genetics; D004330:Drosophila; D029721:Drosophila Proteins; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; C077938:cact protein, Drosophila; C024404:BglII endonuclease; D015252:Deoxyribonucleases, Type II Site-Specific