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42,000-molecular weight EGF receptor has protein kinase activity
Abstract:
The epidermal growth factor (EGF) receptor and other growth factor receptors have been shown to possess tyrosine-specific protein kinase activity. Before the demonstration of kinase activity in growth factor receptors, tyrosine kinases of molecular weight (MW) 60,000 (60K) were found to be encoded by the src oncogene and other oncogenes related to src. Our earlier work on intracellular processing of the EGF receptor, a 170,000-MW polypeptide, provided evidence for proteolytic separation of well defined structural domains, and suggested to us the possibility of separating functional domains by limited proteolysis. The isolation of such kinase domains should facilitate comparison of the receptor/kinase with other well characterized kinases including those of oncogene origin. We report here the identification of a catalytically functional 42K kinase derived proteolytically from the isolated human EGF receptor. This fragment, comparable in size to pp60src, carries the kinase ATP-binding site, and functions catalytically even after detachment from the EGF-binding site and the major autophosphorylation region.
Insights
Researchers isolated a 42K kinase fragment from the epidermal growth factor (EGF) receptor. This catalytically active fragment retains kinase function after separation from the EGF-binding site, aiding comparison with oncogene-related kinases.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Growth factor receptors, like the epidermal growth factor (EGF) receptor, exhibit tyrosine-specific protein kinase activity.
- Prior to this, tyrosine kinases of 60,000 MW (60K) were identified, encoded by the src oncogene and related oncogenes.
- Previous research indicated that the 170,000 MW (170K) EGF receptor undergoes intracellular processing, suggesting domain separation is possible via limited proteolysis.
Purpose of the Study:
- To isolate and characterize functional kinase domains from the EGF receptor.
- To facilitate comparison between the EGF receptor kinase and other characterized kinases, including those from oncogenes.
- To investigate the functional independence of the kinase domain after proteolytic cleavage.
Main Methods:
- Limited proteolysis of the isolated human EGF receptor.
- Biochemical characterization of the resulting proteolytic fragments.
- Assessment of kinase activity and ATP-binding site presence in isolated fragments.
Main Results:
- Identification and isolation of a catalytically functional 42,000 MW (42K) kinase fragment from the human EGF receptor.
- This 42K kinase fragment possesses the ATP-binding site and retains catalytic activity.
- The fragment functions independently, even after detachment from the EGF-binding site and the primary autophosphorylation region.
Conclusions:
- A distinct, catalytically active kinase domain (42K) can be proteolytically derived from the human EGF receptor.
- This isolated kinase domain is comparable in size to pp60src and retains essential kinase functions.
- The findings support the separation of functional domains within the EGF receptor and enable direct comparison with oncogene-encoded tyrosine kinases.