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.
Department of Microbiology, The University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, Texas, 75235-9048, USA.
J S
JS
Brooke
J H
JH
Cha
L
L
Eidels
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