A new member of the ribbon-helix-helix transcription factor superfamily from the plant pathogen Xanthomonas axonopodis pv.citri

• Published in: Journal of structural biology Vol. 170; no. 1; pp. 21 - 31
• Main Authors: Gallo, Mariana, Ferrari, Elena, Eliseo, Tommaso, Amata, Irene, Pertinhez, Thelma A., Katsuyama, Angela M., Paci, Maurizio, Farah, Chuck S., Spisni, Alberto, Cicero, Daniel O.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2010
• Subjects: Amino Acid Sequence; Antitoxin; Base Sequence; Citrus - microbiology; Citrus canker; Dimerization; DNA-binding protein; Electrophoresis, Polyacrylamide Gel; Models, Molecular; Molecular Sequence Data; NMR; Nuclear Magnetic Resonance, Biomolecular; Plasmids - genetics; Protein Conformation; Ribbon-helix-helix fold; Sequence Analysis, DNA; Spectrometry, Fluorescence; Transcription Factors - genetics; Xanthomonas axonopodis - genetics; τci; Ribbon-helix-helix fold; Citrus canker; J; TA; NMR; DNA-binding protein; RHH; Rh; Antitoxin; CSI; Xaa; rmsd; Xac
• ISSN: 1047-8477; 1095-8657
• DOI: 10.1016/j.jsb.2009.12.022

XACb0070 is an uncharacterized protein coded by the two large plasmids isolated from Xanthomonas axonopodis pv. citri, the agent of citrus canker and responsible for important economical losses in citrus world production. XACb0070 presents sequence homology only with other hypothetical proteins belonging to plant pathogens, none of which have their structure determined. The NMR-derived solution structure reveals this protein is a homodimer in which each monomer presents two domains with different structural and dynamic properties: a folded N-terminal domain with βαα topology which mediates dimerization and a long disordered C-terminal tail. The folded domain shows high structural similarity to the ribbon-helix-helix transcriptional repressors, a family of DNA-binding proteins of conserved 3D fold but low sequence homology: indeed XACb0070 binds DNA. Primary sequence and fold comparison of XACb0070 with other proteins of the ribbon-helix-helix family together with examination of the genes in the vicinity of xacb0070 suggest the protein might be the component of a toxin–antitoxin system.