Differences in Crystal and Solution Structures of the Cytolethal Distending Toxin B Subunit: RELEVANCE TO NUCLEAR TRANSLOCATION AND FUNCTIONAL ACTIVATION

• Published in: The Journal of biological chemistry 2006-09, Vol.281 (35), p.25365-25372
• Main Authors: Hontz, Jill S, Villar-Lecumberri, Maria T, Potter, Belinda M, Yoder, Marilyn D, Dreyfus, Lawrence A, Laity, John H
• Format: Article
• Language: English
• Subjects: Active Transport, Cell Nucleus; Arginine - chemistry; Bacterial Toxins - chemistry; Binding Sites; Crystallography, X-Ray; Escherichia; Escherichia coli - metabolism; Magnetic Resonance Spectroscopy; Models, Molecular; Protein Binding; Protein Conformation; Protein Structure, Secondary
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M603727200

Cytolethal distending toxin (CDT) induces cell cycle arrest and apoptosis in eukaryotic cells, which are mediated by the DNA-damaging CdtB subunit. Here we report the first x-ray structure of an isolated CdtB subunit (Escherichia coli-II CdtB, EcCdtB). In conjunction with previous structural and biochemical observations, active site structural comparisons between free and holotoxin-assembled CdtBs suggested that CDT intoxication is contingent upon holotoxin disassembly. Solution NMR structural and ¹⁵N relaxation studies of free EcCdtB revealed disorder in the interface with the CdtA and CdtC subunits (residues Gly²³³-Asp²⁴²). Residues Leu¹⁸⁶-Thr²⁰⁹ of EcCdtB, which encompasses tandem arginine residues essential for nuclear translocation and intoxication, were also disordered in solution. In stark contrast, nearly identical well defined α-helix and β-strand secondary structures were observed in this region of the free and holotoxin CdtB crystallographic models, suggesting that distinct changes in structural ordering characterize subunit disassembly and nuclear localization factor binding functions.