An Arabidopsis SBP-domain fragment with a disrupted C-terminal zinc-binding site retains its tertiary structure

• Published in: FEBS letters Vol. 580; no. 8; pp. 2109 - 2116
• Main Authors: Yamasaki, Kazuhiko, Kigawa, Takanori, Inoue, Makoto, Yamasaki, Tomoko, Yabuki, Takashi, Aoki, Masaaki, Seki, Eiko, Matsuda, Takayoshi, Tomo, Yasuko, Terada, Takaho, Shirouzu, Mikako, Tanaka, Akiko, Seki, Motoaki, Shinozaki, Kazuo, Yokoyama, Shigeyuki
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 03.04.2006
• Subjects: Amino Acid Sequence; Arabidopsis - chemistry; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Binding Sites; Circular Dichroism; DNA - metabolism; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Sequence Data; Peptide Fragments - chemistry; Protein Structure, Tertiary; Protein–DNA interaction; Sequence Alignment; Surface Plasmon Resonance; Transcription factor; Transcription Factors - chemistry; Transcription Factors - metabolism; Zinc - metabolism; Zinc binding; Zinc binding; Arabidopsis thaliana; Transcription factor; Protein–DNA interaction
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/j.febslet.2006.03.014

SQUAMOSA promoter-binding proteins (SBPs) form a major family of plant-specific transcription factors, mainly related to flower development. SBPs share a highly conserved DNA-binding domain of ∼80 amino acids (SBP domain), which contains two non-interleaved zinc-binding sites formed by eight conserved Cys or His residues. In the present study, an Arabidopsis SPL12 SBP-domain fragment that lacks a Cys residue involved in the C-terminal zinc-binding pocket was found to retain a folded structure, even though only a single Zn 2+ ion binds to the fragment. Solution structure of this fragment determined by NMR is very similar to the previously determined structures of the full SBP domains of Arabidopsis SPL4 and SPL7. Considering the previous observations that chelating all the Zn 2+ ions of SBPs resulted in the complete unfolding of the structure and that a mutation of the Cys residue equivalent to that described above impaired the DNA-binding activity, we propose that the Zn 2+ ion at the N-terminal site is necessary to maintain the overall tertiary structure, while the Zn 2+ ion at the C-terminal site is necessary for the DNA binding, mainly by guiding the basic C-terminal loop to correctly fit into the DNA groove.