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 (K(D)) of ≃ 1 x 10-8-10-9 M at 4°C, 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°C 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 K(D) 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.
|Number of pages||6|
|Journal||Biochemical and Biophysical Research Communications|
|Publication status||Published - 1998 Jul 20|
Bibliographical noteFunding Information:
We thank Robert S. Munford, Sergei Popov, and Christine Ward for critical review of the manuscript. We also thank Kathy Potter and Sally Ward for helpful discussions in the early part of these studies. The editorial assistance of Eleanor R. Eidels is greatly appreciated. This research was supported by United States Public Health Service Grant AI-16805.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology