title: Acid-triggered membrane insertion of Pseudomonas exotoxin A involves an original mechanism based on pH-regulated tryptophan exposure.
abstract: Exposure to low endosomal pH during internalization of Pseudomonas exotoxin A (PE) triggers membrane insertion of its translocation domain. This process is a prerequisite for PE translocation to the cytosol where it inactivates protein synthesis. Although hydrophobic helices enable membrane insertion of related bacterial toxins such as diphtheria toxin, the PE translocation domain is devoid of hydrophobic stretches and the structural features triggering acid-induced membrane insertion of PE are not known. Here we have identified a molecular device that enables PE membrane insertion. This process is promoted by exposure of a key tryptophan residue. At neutral pH, this Trp is buried in a hydrophobic pocket closed by the smallest alpha-helix of the translocation domain. Upon acidification, protonation of the Asp that is the N-cap residue of the helix leads to its destabilization, enabling Trp side chain insertion into the endosome membrane. This tryptophan-based membrane insertion system is surprisingly similar to the membrane-anchoring mechanism of human annexin-V and could be used by other proteins as well.
authors.affiliation: Unite Mixte de Recherche 5539 CNRS, Case 107, Département Biologie-Santé, Université Montpellier II, 34095 Montpellier, France.
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Méré
authors.forename: Juliette
authors.initials: J
authors.lastname: Morlon-Guyot
authors.forename: Anne
authors.initials: A
authors.lastname: Bonhoure
authors.forename: Laurent
authors.initials: L
authors.lastname: Chiche
authors.forename: Bruno
authors.initials: B
authors.lastname: Beaumelle
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D019921:Biotinylation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002474:Cell-Free System; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004167:Diphtheria Toxin / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005098:Exotoxins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D000922:Immunotoxins / Q000737:chemistry; D020128:Inhibitory Concentration 50; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011549:Pseudomonas / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D017304:Annexin A5; D002712:Chlorides; D004167:Diphtheria Toxin; D005098:Exotoxins; D000922:Immunotoxins; D002586:Cesium; D001224:Aspartic Acid; D014364:Tryptophan; C028019:cesium chloride