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Phosphorylation of smg p21B/rap1B p21 by cyclic GMP-dependent protein kinase
1Department of Biochemistry, Kobe University School of Medicine, Japan.
Abstract:
smg p21B/rap1B p21, a member of ras p21-like small GTP-binding protein superfamily, has been shown to be phosphorylated by cyclic AMP-dependent protein kinase (protein kinase A). We show here that this protein was also phosphorylated by cyclic GMP-dependent protein kinase (protein kinase G) in a cell-free system. The same serine residue (Ser179) in the C-terminal region was phosphorylated by both protein kinases G and A. The Km and Vmax values of smg p21B for protein kinase G were 5 x 10(-7) M and 4 x 10(-9) mol/min/mg, and those values for protein kinase A were 1 x 10(-7) M and 3 x 10(-8) mol/min/mg.
Insights
Small GTP-binding protein smg p21B is phosphorylated by cyclic GMP-dependent protein kinase (protein kinase G), similar to cyclic AMP-dependent protein kinase (protein kinase A). Both kinases target the same serine residue (Ser179) on smg p21B.
Area of Science:
- Molecular Biology
- Biochemistry
- Signal Transduction
Background:
- Smg p21B/rap1B p21 is a small GTP-binding protein.
- It belongs to the ras p21-like superfamily.
- Previous studies showed phosphorylation by cyclic AMP-dependent protein kinase (protein kinase A).
Purpose of the Study:
- To investigate if cyclic GMP-dependent protein kinase (protein kinase G) also phosphorylates smg p21B.
- To identify the specific phosphorylation site(s).
- To compare the kinetic parameters of phosphorylation by protein kinase G and A.
Main Methods:
- Cell-free phosphorylation assays.
- Identification of phosphorylated serine residue.
- Enzyme kinetics analysis (Km and Vmax determination).
Main Results:
- Smg p21B was phosphorylated by protein kinase G in a cell-free system.
- Phosphorylation occurred at the same serine residue (Ser179) as with protein kinase A.
- Kinetic parameters (Km and Vmax) for protein kinase G and A were determined.
Conclusions:
- Protein kinase G, like protein kinase A, phosphorylates smg p21B at Ser179.
- This suggests a shared regulatory mechanism involving these two kinases.
- Kinetic differences may indicate distinct roles or efficiencies in cellular signaling pathways.