Accessibility changes within diphtheria toxin T domain when in the functional molten globule state, as determined using hydrogen/deuterium exchange measurements.
The translocation domain (T domain) of diphtheria toxin adopts a partially folded state, the so-called molten globule state, to become functional at acidic pH. We compared, using hydrogen/deuterium exchange experiments associated with MS, the structures of the T domain in its soluble folded state at neutral pH and in its functional molten globule state at acidic pH. In the native state, the alpha-helices TH5 and TH8 are identified as the core of the domain. Based on the high-resolution structure of the T domain, we propose that TH8 is highly protected because it is buried within the native structure. According to the same structure, TH5 is partly accessible at the surface of the T domain. We propose that its high protection is caused by the formation of dimers. Within the molten globule state, high protection is still observed within the helical hairpin TH8-TH9, which is responsible for the insertion of the T domain into the membrane. In the absence of the lipid bilayer, this hydrophobic part of the domain self-assembles, leading to the formation of oligomers. Overall, hydrogen/deuterium-exchange measurements allow the analysis of interaction contacts within small oligomers made of partially folded proteins. Such information, together with crystal structure data, are particularly valuable for using to analyze the self-assembly of proteins.
Man
Petr
P
Laboratoire de Spectrométrie de Masse des Protéines, Institut de Biologie Structurale (CEA, CNRS, UJF, UMR 5075), Grenoble, France.
Montagner
Caroline
C
Vitrac
Heidi
H
Kavan
Daniel
D
Pichard
Sylvain
S
Gillet
Daniel
D
Forest
Eric
E
Forge
Vincent
V
D000595:Amino Acid Sequence; D041961:Deuterium Exchange Measurement / Q000379:methods*; D004167:Diphtheria Toxin / Q000737:chemistry* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D004167:Diphtheria Toxin