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The epidermal growth factor receptor as a substrate for a kinase-splitting membranal proteinase
1Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
A brush-border membranal proteinase, which specifically clips the catalytic subunit of cAMP-dependent protein kinase, is shown to cleave the receptor for the epidermal growth factor (EGF) (Mr = 170,000) into two fragments of Mr = 140,000 and 30,000. The 140-kDa fragment retains its EGF-binding site and its EGF-dependent protein tyrosine kinase activity on exogenous substrates, but it loses its capacity to undergo self-phosphorylation. It is shown to be distinct from the 150-kDa fragment of the EGF receptor obtained by the Ca2+-activated neutral proteinase. The membranal proteinase strictly recognizes the native structure of the receptor and fails to cleave either the denatured receptor or its 150-kDa degradation product. Thus the membranal proteinase acts as a conformation-recognizing probe for both the protein-tyrosine kinase domain of the EGF receptor and the catalytic subunit of cAMP-dependent protein-Ser/Thr kinase, suggesting that the known sequence homology between these two kinases is also reflected in their conformation. The well defined 140-kDa fragment described here is useful for structure-function studies of the EGF receptor.
Insights
A novel brush-border enzyme cleaves the epidermal growth factor (EGF) receptor into two fragments. The larger fragment retains EGF binding and kinase activity, aiding structure-function studies.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- The epidermal growth factor (EGF) receptor is a key signaling molecule.
- Protein kinases play crucial roles in cellular processes.
- Understanding receptor processing is vital for cell signaling research.
Purpose of the Study:
- To investigate the cleavage of the EGF receptor by a specific brush-border membranal proteinase.
- To characterize the functional properties of the resulting EGF receptor fragments.
- To explore the conformational recognition of protein kinases by the membranal proteinase.
Main Methods:
- Enzymatic cleavage of the EGF receptor using a brush-border membranal proteinase.
- Analysis of protein fragments by molecular weight (Mr).
- Assays for EGF-binding and protein tyrosine kinase activity.
- Comparison with fragments generated by other proteases.
Main Results:
- The membranal proteinase cleaved the 170-kDa EGF receptor into 140-kDa and 30-kDa fragments.
- The 140-kDa fragment retained EGF-binding and kinase activity but lost self-phosphorylation.
- This fragment is distinct from those produced by Ca2+-activated neutral proteinase.
- The enzyme specifically recognizes the native receptor structure.
Conclusions:
- The brush-border membranal proteinase acts as a conformation-recognizing probe for EGF receptor and cAMP-dependent protein kinase.
- Sequence homology between kinases may extend to conformational similarities.
- The 140-kDa fragment is a valuable tool for EGF receptor structure-function studies.