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 ...
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.
Related Citations:
Crystallization of Exotoxin A from Pseudomonas aeruginosa Collier, R.J., McKay, D.B. (1982) J Mol Biol 157: 413
Structure of Exotoxin A of Pseudomonas aeruginosa at 3.0-Angstrom Resolution Allured, V.S., Collier, R.J., Carroll, S.F., McKay, D.B. (1986) Proc Natl Acad Sci U S A 83: 1320
Mapping the Enzymatic Active Site of Pseudomonas aeruginosa Exotoxin A Brandhuber, B.J., Allured, V.S., G., Falbel T., B., McKay D. (1988) Proteins 3: 146
The Crystal Structure of Pseudomonas aeruginosa Exotoxin Domain III with Nicotinamide and AMP: conformational differences with the intact exotoxin Li, M., Dyda, F., Benhar, I., Pastan, I., Davies, D.R. (1995) Proc Natl Acad Sci U S A 92: 9308
Organizational Affiliation:
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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