Phosphorylation in the Regulation of Protein Phosphatases
Cell cycles are controlled by the cycling of proteins through phosphorylation and dephosphorylation. These reactions are catalyzed by kinases and phosphatases that are now appreciated as being highly specific. Dephosphorylation is not the simple reverse of phosphorylation because the introduction of a phosphate group will lead to formation of hydrogen bonds with the guanidinium side chains of arginine residues, accompanied by a refolding of the protein (1). The phosphorylated site then occupies a new position on the protein surface hydrogen-bonded to a portion of the protein distant from the original location of the unphosphorylated site. Phosphatases recognize the new conformation and hydrolyze the phosphate, abolishing the hydrogen bonds formed following phosphorylation, thereby reversing the conformational change. The cycle of phosphorylation and dephosphorylation functions as a molecular switch at appropriate times during the cell cycle and in response to extracellular signals (Figure 1A).
KeywordsTyrosine Adenosine Fractionation Serine Trypsin
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