Biochemistry Online: An Approach Based on Chemical Logic

Biochemistry Online





Learning Goals/Objectives for Chapter 9C:
After class and this reading, students will be able to

  • define kinases and phosphatases and their role in signal transduction
  • define primary and secondary messengers and give specific examples of each
  • describe the role of G proteins in coupling ligand induced conformational changes in the bound receptor to activation of specific effector proteins such as adenylate cyclase and phospholipase
  • differentiate between kinases activated by second messengers and those activated by primary messengers (ligand-gated receptor Tyr kinases)
  • describe the structural characteristics of G protein coupled serpentine receptors and ligand gated receptor tyrosine kinases
  • draw a diagram showing the general features of kinases mediated signal transduction pathways that lead to activation of gene expression
  • differentiate between neuron responses mediated by neurotransmitters on binding gated receptor/ion channels compares to G-protein coupled receptors

Estonian Translation by Anna Galovich

C5.  Protein Kinase G (PKG)

Cascade of events:  A transmembrane receptor OR a cytoplasmic protein  WITH LIGAND-DEPENDENT ENZYMATIC ACTIVITY (guanylate cyclase) binds an extracellular chemical signal (for the transmembrane receptor) or an intracellular ligand (for the cytoplasmic protein receptor), causing a conformational change in the receptor.  The bound receptor is now a guanylate cyclase which converts GTP into cyclic GMP. This second messenger, like cAMP which binds to and activates PKA,  binds to and activates the cGMP-dependent protein kinase (PKG).  An example of a hormone which works through a transmembrane receptor is atrial naturetic factor, which binds to a cell-surface receptor whose shape change is communicated to the intracellular receptor domain through the single transmembrane helix, leading to the activation of the intracelluar guanylate cyclase domain of the protein.   Likewise, nitric oxide, NO, a gaseous ligand formed from Arg, can diffuse through the cell membrane, where it binds to the heme of a cytoplasmic receptor/guanylate cyclase which form cGMP, leading to activation of PKG. (Steroid hormones also enter the cell where they interact with a cytoplasmic receptor which often acts as steroid hormone-dependent transcription factor. )

Cell Signaling Technologies:  A Great Source of Information on Kinases

Kinase inhibitors

Kinases: Evolution of Dynamic Regulatory Proteins

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