1. BIOL 5190/6190 Cellular & Molecular Singal Transduction
Lecture 03 – General aspects of molecular signaling pathways and cellular signaling
BIOL 5190/6190 Cellular & Molecular Singal Transduction
Prepared by Bob Locy
Last modified -13F

2. G Protein Coupled Receptor Pathways
G Protein Coupled Receptors
Seven membrane-spanning domain receptors
Heterotrimeric G-proteins
Activate different second-messenger systems
cyclic AMP based
IP3 based
Second messengers work to modulate effectors that mediate cellular responses

3. General principle of the GPCR signaling system.
(B) Following ligand binding, the receptor undergoes conformational changes, which promote the coupling with heterotrimeric G proteins (Gαβγ), and catalyzes the exchange of GDP for GTP on the α-subunit. This event triggers conformational and/or dissociation events between the α-subunit and βγ-subunit. GαS activates adenylyl cyclases, leading to cAMP synthesis, which in turn activates protein kinase A (PKA). Gαq activates phospholipase C, which cleaves phosphatidylinositol (4,5)-bisphosphate (PIP2) into diacylglycerol (DAG) and inositol (1,4,5)-trisphosphate (IP3). IP3 then diffuses through the cytosol and activates IP3-gated Ca2+ channels in the membranes of the endoplasmic reticulum, causing the release of stored Ca2+ into the cytosol. The increase of cytosolic Ca2+ promotes PKC translocation to the plasma membrane, and then activation by DAG. Activation of Gi blocks adenylyl-cyclase-mediated cAMP synthesis by its α-subunits, whereas Gβγ-mediated signaling processes such as activation of G-protein-regulated inwardly rectifying potassium (GIRK) channels. VSCC, voltage-sensitive Ca2+ channel.
General principle of the GPCR signaling system. (A) Molecular representation of a GPCR in complex with a Gαβγ, based on crystal structures of rhodopsin (red; coordinates from PDB code 1GZM) and the inactive heterotrimeric Gi protein (from PDB 1GG2).
Vilardaga J et al. J Cell Sci 2010;123:
©2010 by The Company of Biologists Ltd

4. GPCRs
(B) Following ligand binding, the receptor undergoes conformational changes, which promote the coupling with heterotrimeric G proteins (Gαβγ), and catalyzes the exchange of GDP for GTP on the α-subunit. This event triggers conformational and/or dissociation events between the α-subunit and βγ-subunit. GαS activates adenylyl cyclases, leading to cAMP synthesis, which in turn activates protein kinase A (PKA). Gαq activates phospholipase C, which cleaves phosphatidylinositol (4,5)-bisphosphate (PIP2) into diacylglycerol (DAG) and inositol (1,4,5)-trisphosphate (IP3). IP3 then diffuses through the cytosol and activates IP3-gated Ca2+ channels in the membranes of the endoplasmic reticulum, causing the release of stored Ca2+ into the cytosol. The increase of cytosolic Ca2+ promotes PKC translocation to the plasma membrane, and then activation by DAG. Activation of Gi blocks adenylyl-cyclase-mediated cAMP synthesis by its α-subunits, whereas Gβγ-mediated signaling processes such as activation of G-protein-regulated inwardly rectifying potassium (GIRK) channels. VSCC, voltage-sensitive Ca2+ channel.
Vilardaga J et al. J Cell Sci 2010;123:

5. Modulation of G-protein signaling by receptor heterodimers.
Modulation of G-protein signaling by receptor heterodimers. Representation of the α2A-AR (red)–MOR (blue) heterodimer complex based on the crystal structure of rhodopsin (coordinates from PDB code 1GZM), and chemical structures of norepinephrine and morphine. G-protein signaling mediated by the receptor heterodimer in response to norepinephrine or morphine is modulated by the simultaneous action of both signaling ligands. This modulation proceeds through conformational changes (arrows) that propagate from one receptor to the other with a half-life of 400 mseconds.
Vilardaga J et al. J Cell Sci 2010;123:
©2010 by The Company of Biologists Ltd

6. Module 1: Figure stimuli for cyclic AMP signalling
Cell Signalling Biology - Michael J. Berridge

7. Module 1: Figure stimuli for InsP3/DAG signalling
Cell Signalling Biology - Michael J. Berridge

8. Tyrosine and histidine kinases
Histidine kinase receptors are among most widely known types of receptors.
Also known as phosphorelay receptors

9. Figure 1 Two-component histidine kinases and more complex phosphorelay systems
Biochemical Society Transactions (2013) 41, Paul V. Attwood

10. Tyrosine and Histidine Kinase Receptors
Approximately 20 different Receptor Tyrosine Kinase classes have been identified. [KEGG, 2010]
RTK class I (EGF receptor family) (ErbB family) RTK class X (LTK receptor family)
RTK class II (Insulin receptor family) RTK class XI (TIE receptor family)
RTK class III (PDGF receptor family) RTK class XII (ROR receptor family)
RTK class IV (FGF receptor family) RTK class XIII (DDR receptor family)
RTK class V (VEGF receptors family) RTK class XIV (RET receptor family)
RTK class VI (HGF receptor family) RTK class XV (KLG receptor family)
RTK class VII (Trk receptor family) RTK class XVI (RYK receptor family)
RTK class VIII (Eph receptor family) RTK class XVII (MuSK receptor family)
RTK class IX (AXL receptor family)
Tyrosine and Histidine Kinase Receptors

11. Tyrosine and Histidine Kinase Receptors
Most RTKs are single subunit receptors but some exist as multimeric complexes, e.g., the insulin receptor that forms disulfide-linked dimers in the absence of hormone
Ligand binding to the extracellular domain often induces formation of receptor dimers.
Each monomer has a single hydrophobic transmembrane- spanning domain composed of amino acids, an extracellular N-terminal region, and an intracellular C-terminal region.
The extracellular N-terminal region exhibits a variety of conserved elements including immunoglobulin (Ig)-like or epidermal growth factor (EGF)-like domains, fibronectin type III repeats, or cysteine-rich regions that are characteristic for each subfamily of RTKs; these domains contain primarily a ligand-binding site, which binds extracellular ligands, e.g., a particular growth factor or hormone.
The intracellular C-terminal region displays the highest level of conservation and comprises catalytic domains responsible for the kinase activity of these receptors, which catalyses receptor autophosphorylation and tyrosine phosphorylation of RTK substrates.

12. Module 1: Figure stimuli for enzyme-linked receptors
Cell Signalling Biology - Michael J. Berridge

13. Module 1: Figure tyrosine kinase-linked receptors
Cell Signalling Biology - Michael J. Berridge

14. Module 1: Figure PDGFR activation
Cell Signalling Biology - Michael J. Berridge