PMID: 2111323May 25, 1990Paper

Involvement of denaturation-like changes in Pseudomonas exotoxin a hydrophobicity and membrane penetration determined by characterization of pH and thermal transitions. Roles of two distinct conformationally altered states.

The Journal of Biological Chemistry
J X Jiang, E London

Abstract

Previous investigators have shown that exotoxin A undergoes a conformational switch to a hydrophobic state at low pH. This change appears to play a role in exotoxin A entry into cells by facilitating its penetration of the membranes of acidic organelles. We have examined the effects of pH, temperature, and denaturants in order to define the role of conformational changes in membrane penetration by the exotoxin. We find that two distinct low pH conformations exist. An intermediate low pH state (LI) dominates at pH 3.7-5.4 and is distinguished by blue-shifted fluorescence and weak or no hydrophobicity. The second low pH state (LII) is dominant below pH 3.7 and is characterized by red shifted fluorescence and strong hydrophobicity. LI is a folded state as judged by its spectroscopic properties and the observation that it undergoes distinct and cooperative thermal and denaturant induced unfolding transitions. LII appears to be more like a denatured state, as it shows no cooperative thermal or denaturant induced transitions and has spectroscopic properties very similar to exotoxin A that has been thermally denatured at pH 7. Exotoxin A in the LII state strongly binds detergent micelles and binds and inserts into model membranes. The...Continue Reading

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