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cGMP-dependent protein kinase or Protein Kinase G (PKG) is a serine/threonine-specific protein kinase that is activated by cGMP. It phosphorylates a number of biologically important targets and is implicated in the regulation of smooth muscle relaxation, platelet function, sperm metabolism, cell division, and nucleic acid synthesis. ==Genes and proteins== PKG are serine/threonine kinases that are present in a variety of eukaryotes ranging from the unicellular organism ''Paramecium'' to humans. Two PKG genes, coding for PKG type I (PKG-I) and type II (PKG-II), have been identified in mammals. The N-terminus of PKG-I is encoded by two alternatively spliced exons that specify for the PKG-Iα and PKG-Iβ isoforms. PKG-Iβ is activated at ~10-fold higher cGMP concentrations than PKG-Iα. The PKG-I and PKG-II are homodimers of two identical subunits (~75 kDa and ~85 kDa, respectively) and share common structural features. Each subunit is composed of three functional domains: * (1) an ''N-terminal domain'' that mediates homodimerization, suppression of the kinase activity in the absence of cGMP, and interactions with other proteins including protein substrates * (2) a ''regulatory domain'' that contains two non-identical cGMP-binding sites * (3) a ''kinase domain'' that catalyzes the phosphate transfer from ATP to the hydroxyl group of a serine/threonine side chain of the target protein Binding of cGMP to the regulatory domain induces a conformational change which stops the inhibition of the catalytic core by the N-terminus and allows the phosphorylation of substrate proteins. Whereas PKG-I is predominantly localized in the cytoplasm, PKG-II is anchored to the plasma membrane by N-terminal myristoylation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CGMP-dependent protein kinase」の詳細全文を読む スポンサード リンク
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