Diphtheria toxin:receptor interaction: association, dissociation, and effect of pH.
Diphtheria toxin (DT) binds to a specific heparin-binding epidermal growth factor-like growth factor (HB-EGF) precursor that is expressed in DT-sensitive cells. DT binds to the cell-surface HB-EGF precursor with an apparent dissociation constant (KD) of approximately 1 x 10(-8) - 10(-9) M at 4 degreesC, a temperature at which toxin binds but is not internalized. The interaction of DT with the cell-surface receptor, however, may be influenced by other cell-surface components. We used a biosensor method to measure the binding of DT to immobilized recombinant human HB-EGF (hHB-EGF) at 25 degreesC with no other cellular components present. We observed that at pH 7.4, using this in vitro two component system, DT binds to hHB-EGF with an apparent KD of 2.7 x 10(-8) M. We also observed that the dissociation of DT from hHB-EGF at pH values that approach those of the endosome occurs at a faster rate as the pH is decreased. These results suggest that the low pH of the endosome is sufficient to allow DT to dissociate from the HB-EGF precursor, prior to the translocation of the enzymatically active fragment of DT into the cytosol.
Brooke
J S
JS
Department of Microbiology, The University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, Texas, 75235-9048, USA.
Cha
J H
JH
Eidels
L
L
D015374:Biosensing Techniques; D004167:Diphtheria Toxin / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D006863:Hydrogen-Ion Concentration; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D011485:Protein Binding / Q000502:physiology; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013696:Temperature
D004167:Diphtheria Toxin; C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins