Download MendeleyRefined Crystallographic Structure of Pseudomonas aeruginosa Exotoxin A and its Implications for the Molecular Mechanism of Toxicity
Wedekind, J.E., Trame, C.B., Dorywalska, M., Koehl, P., Raschke, T.M., McKee, M., FitzGerald, D., Collier, R.J., McKay, D.B.(2001) J Mol Biol 314: 823-837
- PubMed: 11734000
- DOI: https://doi.org/10.1006/jmbi.2001.5195
- Primary Citation of Related Structures:
1IKP, 1IKQ - PubMed Abstract:
Exotoxin A of Pseudomonas aeruginosa asserts its cellular toxicity through ADP-ribosylation of translation elongation factor 2, predicated on binding to specific cell surface receptors and intracellular trafficking via a complex pathway that ultimately results in translocation of an enzymatic activity into the cytoplasm. In early work, the crystallographic structure of exotoxin A was determined to 3.0 A resolution, revealing a tertiary fold having three distinct structural domains; subsequent work has shown that the domains are individually responsible for the receptor binding (domain I), transmembrane targeting (domain II), and ADP-ribosyl transferase (domain III) activities, respectively. Here, we report the structures of wild-type and W281A mutant toxin proteins at pH 8.0, refined with data to 1.62 A and 1.45 A resolution, respectively. The refined models clarify several ionic interactions within structural domains I and II that may modulate an obligatory conformational change that is induced by low pH. Proteolytic cleavage by furin is also obligatory for toxicity; the W281A mutant protein is substantially more susceptible to cleavage than the wild-type toxin. The tertiary structures of the furin cleavage sites of the wild-type and W281 mutant toxins are similar; however, the mutant toxin has significantly higher B-factors around the cleavage site, suggesting that the greater susceptibility to furin cleavage is due to increased local disorder/flexibility at the site, rather than to differences in static tertiary structure. Comparison of the refined structures of full-length toxin, which lacks ADP-ribosyl transferase activity, to that of the enzymatic domain alone reveals a salt bridge between Arg467 of the catalytic domain and Glu348 of domain II that restrains the substrate binding cleft in a conformation that precludes NAD+ binding. The refined structures of exotoxin A provide precise models for the design and interpretation of further studies of the mechanism of intoxication.
Organizational Affiliation:
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
