title: Solution and membrane-bound chaperone activity of the diphtheria toxin translocation domain towards the catalytic domain.
abstract: During cell intoxication by diphtheria toxin, endosome acidification triggers the translocation of the catalytic (C) domain into the cytoplasm. This event is mediated by the translocation (T) domain of the toxin. Previous work suggested that the T domain acts as a chaperone for the C domain during membrane penetration of the toxin. Using partitioning experiments with lipid vesicles, fluorescence spectroscopy, and a lipid vesicle leakage assay, we characterized the dominant behavior of the T domain over the C domain during the successive steps by which these domains interact with a membrane upon acidification: partial unfolding in solution and during membrane binding, and then structural rearrangement during penetration into the membrane. To this end, we compared, for each domain, isolated or linked together in a CT protein (the toxin lacking the receptor-binding domain), each of these steps. The behavior of the T domain is marginally modified by the presence or absence of the C domain, whereas that of the C domain is greatly affected by the presence of the T domain . All of the steps leading to membrane penetration of the C domain are triggered at higher pH by the T domain , by 0.5-1.6 pH units. The T domain stabilizes the partially folded states of the C domain corresponding to each step of the process. The results unambiguously demonstrate that the T domain acts as a specialized pH-dependent chaperone for the C domain. Interestingly, this chaperone activity acts on very different states of the protein: in solution, membrane-bound, and membrane-inserted.
authors.affiliation: Commissariat à l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay (iBiTecS), Service d'Ingénierie Moléculaire des Protéines (SIMOPRO), Gif sur Yvette, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Chassaing
authors.forename: Sylvain
authors.initials: S
authors.lastname: Pichard
authors.forename: Anne
authors.initials: A
authors.lastname: Araye-Guet
authors.forename: Julien
authors.initials: J
authors.lastname: Barbier
authors.forename: Vincent
authors.initials: V
authors.lastname: Forge
authors.forename: Daniel
authors.initials: D
authors.lastname: Gillet
mesh_terms: D020134:Catalytic Domain; D003593:Cytoplasm / Q000378:metabolism; D004167:Diphtheria Toxin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D018832:Molecular Chaperones / Q000737:chemistry*; D010539:Permeability; D011487:Protein Conformation; D021381:Protein Transport; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D053835:Unilamellar Liposomes / Q000737:chemistry
chemical_list: D004167:Diphtheria Toxin; D018832:Molecular Chaperones; D012996:Solutions; D053835:Unilamellar Liposomes