title: Alanine zipper-like coiled-coil domains are necessary for homotypic dimerization of plant GAGA-factors in the nucleus and nucleolus.
abstract: GAGA-motif binding proteins control transcriptional activation or repression of homeotic genes. Interestingly, there are no sequence similarities between animal and plant proteins. Plant BBR/BPC-proteins can be classified into two distinct groups: Previous studies have elaborated on group I members only and so little is known about group II proteins. Here, we focused on the initial characterization of AtBPC6, a group II protein from Arabidopsis thaliana. Comparison of orthologous BBR/BPC sequences disclosed two conserved signatures besides the DNA binding domain. A first peptide signature is essential and sufficient to target AtBPC6-GFP to the nucleus and nucleolus. A second domain is predicted to form a zipper-like coiled-coil structure. This novel type of domain is similar to Leucine zippers, but contains invariant alanine residues with a heptad spacing of 7 amino acids. By yeast-2-hybrid and BiFC-assays we could show that this Alanine zipper domain is essential for homotypic dimerization of group II proteins in vivo. Interhelical salt bridges and charge-stabilized hydrogen bonds between acidic and basic residues of the two monomers are predicted to form an interaction domain, which does not follow the classical knobs-into-holes zipper model. FRET-FLIM analysis of GFP/RFP-hybrid fusion proteins validates the formation of parallel dimers in planta. Sequence comparison uncovered that this type of domain is not restricted to BBR/BPC proteins, but is found in all kingdoms.
authors.affiliation: Center of Plant Molecular Biology (ZMBP) Plant Physiology, University of Tübingen, Tübingen, Germany. dierk.wanke@zmbp.uni-tuebingen.de
authors.forename: Dierk
authors.initials: D
authors.lastname: Wanke
authors.forename: Mareike L
authors.initials: ML
authors.lastname: Hohenstatt
authors.forename: Marek
authors.initials: M
authors.lastname: Dynowski
authors.forename: Ulrich
authors.initials: U
authors.lastname: Bloss
authors.forename: Andreas
authors.initials: A
authors.lastname: Hecker
authors.forename: Kirstin
authors.initials: K
authors.lastname: Elgass
authors.forename: Sabine
authors.initials: S
authors.lastname: Hummel
authors.forename: Achim
authors.initials: A
authors.lastname: Hahn
authors.forename: Katharina
authors.initials: K
authors.lastname: Caesar
authors.forename: Frank
authors.initials: F
authors.lastname: Schleifenbaum
authors.forename: Klaus
authors.initials: K
authors.lastname: Harter
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Berendzen
mesh_terms: D021581:Active Transport, Cell Nucleus; D000409:Alanine; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000166:cytology*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D002466:Cell Nucleolus / Q000378:metabolism*; D019295:Computational Biology; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry; D006801:Humans; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010802:Phylogeny; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000166:cytology; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D014157:Transcription Factors / Q000737:chemistry
chemical_list: D029681:Arabidopsis Proteins; C571064:BPC6 protein, Arabidopsis; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D014157:Transcription Factors; C063460:Trl protein, Drosophila; D000409:Alanine