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Protein kinase C-associated kinase (PKK), a novel membrane-associated, ankyrin repeat-containing protein kinase
1Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Abstract:
A novel murine membrane-associated protein kinase, PKK (protein kinase C-associated kinase), was cloned on the basis of its physical association with protein kinase Cbeta (PKCbeta). The regulated expression of PKK in mouse embryos is consistent with a role for this kinase in early embryogenesis. The human homolog of PKK has over 90% identity to its murine counterpart, has been localized to chromosome 21q22.3, and is identical to the PKCdelta-interacting kinase, DIK (Bahr, C., Rohwer, A., Stempka, L., Rincke, G., Marks, F., and Gschwendt, M. (2000) J. Biol. Chem. 275, 36350-36357). PKK comprises an N-terminal kinase domain and a C-terminal region containing 11 ankyrin repeats. PKK exhibits protein kinase activity in vitro and associates with cellular membranes. PKK exists in three discernible forms at steady state: an underphosphorylated form of 100 kDa; a soluble, cytosolic, phosphorylated form of 110 kDa; and a phosphorylated, detergent-insoluble form of 112 kDa. PKK is initially synthesized as an underphosphorylated soluble 100-kDa protein that is quantitatively converted to a detergent-soluble 110-kDa form. This conversion requires an active catalytic domain. Although PKK physically associates with PKCbeta, it does not phosphorylate this PKC isoform. However, PKK itself may be phosphorylated by PKCbeta. PKK represents a developmentally regulated protein kinase that can associate with membranes. The functional significance of its association with PKCbeta remains to be ascertained.
Insights
A novel protein kinase C-associated kinase (PKK) was identified, showing regulated expression in mouse embryos, suggesting a role in early development. Its association with protein kinase Cbeta (PKCbeta) and membrane localization were characterized.
Area of Science:
- Molecular Biology
- Biochemistry
- Developmental Biology
Background:
- Protein kinase Cbeta (PKCbeta) is a key signaling molecule.
- The discovery of novel kinases associated with PKC signaling pathways is crucial for understanding cellular regulation.
Purpose of the Study:
- To clone and characterize a novel kinase associated with PKCbeta.
- To investigate the expression, localization, and enzymatic activity of the novel kinase, named PKK.
- To explore the relationship between PKK and PKCbeta.
Main Methods:
- Cloning of the murine PKK gene based on physical association with PKCbeta.
- Analysis of PKK expression in mouse embryos.
- Biochemical assays to determine kinase activity and phosphorylation states.
- Subcellular localization studies (membrane association).
Main Results:
- A novel membrane-associated protein kinase, PKK, was cloned and characterized.
- PKK exhibits regulated expression in mouse embryos, suggesting a role in embryogenesis.
- PKK possesses kinase activity, associates with membranes, and exists in multiple phosphorylation states.
- PKK associates with PKCbeta but does not phosphorylate it; PKK may be phosphorylated by PKCbeta.
Conclusions:
- PKK is a developmentally regulated protein kinase with membrane-associating properties.
- The physical association between PKK and PKCbeta suggests a potential functional link, though its significance requires further investigation.
- The human homolog of PKK is located on chromosome 21q22.3.