Receptors, ligands and signal transduction

Course overview

A comprehensive investigation of receptor pharmacology, binding thermodynamics, GPCR dynamics, receptor tyrosine kinases, second messenger cascades, and biased agonism.

Track

Mechanism bridge

Level

Core course

Lessons

12

Estimated duration

75 min

Scientific review panel

Receptor Pharmacology

Models equilibrium binding, Kd, EC50, fractional receptor occupancy, and spare receptors.

Structural Biology

Analyzes 7-transmembrane GPCR conformational states, G-protein coupling, and arrestin binding.

Signal Transduction

Traces cAMP/PKA, IP3/DAG/PKC, MAP kinase, and PI3K/Akt intracellular cascades.

Chemical Sequence Pharmacology

Evaluates synthetic sequence affinity, receptor selectivity, and biased signaling in research models.

Complete course curriculum (12 lessons)

1. Lesson 1

   Thermodynamics of Receptor-Ligand Binding

   Learning objective:

   Understand equilibrium dissociation constant (Kd), fractional occupancy, and binding kinetics.

   Core mechanism:

   Ligand-receptor interactions obey the law of mass action. Fractional occupancy is defined by [L] / ([L] + Kd). When [L] = Kd, 50% of receptors are occupied.

   Key takeaway:

   Kd measures binding affinity; lower Kd values reflect tighter ligand-receptor binding.

2. Lesson 2

   Agonism, Antagonism, Partial Agonism & Inverse Agonism

   Learning objective:

   Distinguish intrinsic efficacy from binding affinity.

   Core mechanism:

   Full agonists stabilize active receptor conformations (efficacy = 1). Partial agonists produce submaximal response. Antagonists bind without activation (efficacy = 0). Inverse agonists reduce basal constitutive receptor activity.

   Key takeaway:

   Affinity determines receptor binding; intrinsic efficacy determines the biological response generated.

3. Lesson 3

   Allosteric Modulation & Receptor Cooperativity

   Learning objective:

   Examine positive (PAM) and negative (NAM) allosteric modulators.

   Core mechanism:

   Allosteric ligands bind topographically distinct non-orthosteric sites, altering receptor conformation to modulate orthosteric ligand affinity, efficacy, or both.

   Key takeaway:

   Allosteric modulators tune endogenous physiological signaling without activating the receptor in isolation.

4. Lesson 4

   G-Protein-Coupled Receptors (GPCRs): Architecture & G-Alpha Subfamilies

   Learning objective:

   Map the 7-transmembrane GPCR superfamily and Gs, Gi/o, Gq/11, and G12/13 coupling.

   Core mechanism:

   Ligand binding induces conformational rearrangement of transmembrane helices, promoting GDP-GTP exchange on the G-alpha subunit and dissociation of G-beta/gamma dimers.

   Key takeaway:

   The specific G-alpha subunit determines downstream second messenger activation.

5. Lesson 5

   Receptor Tyrosine Kinases (RTKs) & Growth Factor Cascades

   Learning objective:

   Trace ligand-induced dimerization, autophosphorylation, and MAPK/Akt signaling.

   Core mechanism:

   Ligand binding (e.g. Insulin, IGF-1, EGF) promotes receptor dimerization and cross-phosphorylation of cytoplasmic tyrosine residues, creating SH2-domain docking sites for Grb2/SOS and PI3K.

   Key takeaway:

   RTK autophosphorylation initiates dual Ras-Raf-MEK-ERK and PI3K-Akt signaling cascades controlling growth and metabolism.

6. Lesson 6

   Cytokine Receptors & The JAK-STAT Pathway

   Learning objective:

   Understand non-catalytic cytokine receptors and direct nuclear transcription activation.

   Core mechanism:

   Cytokine binding oligomerizes receptor chains, activating associated Janus Kinases (JAKs) to phosphorylate receptor tails, recruiting STATs for phosphorylation, dimerization, and nuclear translocation.

   Key takeaway:

   The JAK-STAT pathway provides a direct, rapid conduit from cell-surface cytokine binding to gene transcription.

7. Lesson 7

   Nuclear & Intracellular Receptors

   Learning objective:

   Examine steroid, thyroid, and PPAR transcription factor dynamics.

   Core mechanism:

   Lipophilic ligands cross the plasma membrane to bind cytoplasmic or nuclear receptors, inducing heat shock protein dissociation, dimerization, and binding to Hormone Response Elements (HREs) on DNA.

   Key takeaway:

   Nuclear receptors act as ligand-activated transcription factors with delayed, sustained genomic effects.

8. Lesson 8

   Ion-Channel-Coupled Receptors (Ligand-Gated Channels)

   Learning objective:

   Analyze millisecond-scale synaptic transmission and electrochemical flux.

   Core mechanism:

   Binding of neurotransmitters (e.g. Acetylcholine, GABA, Glutamate) induces allosteric channel opening, permitting selective passage of Na+, K+, Ca2+, or Cl- ions down their electrochemical gradients.

   Key takeaway:

   Ligand-gated ion channels mediate the fastest signaling events in excitable tissues.

9. Lesson 9

   Second Messenger Systems: cAMP, IP3, DAG & Calcium

   Learning objective:

   Trace intracellular amplification cascades.

   Core mechanism:

   Gs activates Adenylyl Cyclase to generate cAMP, activating PKA. Gq activates Phospholipase C-beta to cleave PIP2 into IP3 (releasing ER Ca2+) and DAG (activating PKC).

   Key takeaway:

   Second messengers amplify single ligand-binding events into millions of downstream phosphorylation reactions.

10. Lesson 10

    Signal Amplification, Cross-talk & Network Feedback

    Learning objective:

    Map regulatory loops preventing excessive signal duration.

    Core mechanism:

    Phosphatases, phosphodiesterases (PDEs), and regulator of G-protein signaling (RGS) proteins terminate signaling, while kinase cross-phosphorylation integrates multiple receptor inputs.

    Key takeaway:

    Cellular signaling behaves as a complex, feedback-regulated biological circuit rather than a linear wire.

11. Lesson 11

    Receptor Desensitization, Internalization & Biased Agonism

    Learning objective:

    Examine GRK phosphorylation, beta-arrestin recruitment, and pathway-selective signaling.

    Core mechanism:

    G-protein Receptor Kinases (GRKs) phosphorylate activated GPCRs, recruiting beta-arrestin to uncouple G-proteins and promote clathrin-mediated endocytosis. “Biased agonists” selectively activate G-protein vs arrestin pathways.

    Key takeaway:

    Biased ligands provide functional selectivity, isolating therapeutic signaling from adverse desensitization pathways.

12. Lesson 12

    Sequence Pharmacology: Incretin, Epithalon & GHK-Cu Research Models

    Learning objective:

    Review chemical sequence receptor targets in research literature.

    Core mechanism:

    Evaluates synthetic chemical sequences (Semaglutide at GLP-1R, Epithalon in telomerase modulation, GHK-Cu in extracellular matrix remodeling) as molecular probes in cellular pharmacological assays.

    Key takeaway:

    Receptor pharmacology principles govern all synthetic chemical sequence interactions in non-clinical research.