Lecture 13 (II) - Membranes and Signalling I (April 3) PDF

LECTURE 13 W24 Module 4 Module 5 BIOC*4580 – Membrane Biochemistry Winter 2024 Membranes and Signalling Lehninger Chapter 12 Signals initiate at the membrane Signaling molecules are generally released by one of three general mechanisms: 1. Exocytosis the signal molecule is stored in secretory vesicl...

LECTURE 13 W24 Module 4 Module 5 BIOC*4580 – Membrane Biochemistry Winter 2024 Membranes and Signalling Lehninger Chapter 12 Signals initiate at the membrane Signaling molecules are generally released by one of three general mechanisms: 1. Exocytosis the signal molecule is stored in secretory vesicles, and released upon a signal, (e.g. insulin) this is the main route in eukaryotes 2. Cleavage the signal is part of a protein that is released from its parent membrane by proteolysis, or by cleavage of a GPI anchor (e.g. epidermal growth factor) 3. ABC transporter signal molecule exits the cell via an ABC transporter (e.g. prostaglandins) G-Protein Coupled Receptor (GPCR) signaling In multicellular animals, GPCRs are the largest group of plasma membrane receptors. (>800 GPCRs in the human genome) Consists of 3 components: 1) Plasma membrane receptor with 7 transmembrane helices 2) heterotrimeric guanosine nucleotide-binding protein (G protein) 3) Effecter enzyme in the plasma membrane that generates a 2nd messenger Second Messengers include: -cAMP -cGMP -inositol 1,4,5-trisphosphate (PIP3) 4 GPCR Topology 7 TM Helices, often additional extra-membrane helices in IL/EL loops N-terminus is extracellular, C-terminus is intracellular 3 intracellular loops (IL1->3), 3 extracellular loops (EL1->3) Disulfide bonds typically connect EL1-EL2, and EL2-EL3 EL2 (the gate) controls access to ligand binding site Helix 8 lies along the membrane surface, and is amphipathic and lipidylated Note TM3 is in center, other helices wrap around it Kimber, after Buehlar Key GPCR architectural features The outer leaflet portion contains the ligand binding site This region is diverse between families Shifts here are small upon binding (typically 1 Å or less) The inner leaflet portion is more conserved, and forms a signaling module Here large conformational changes convey the signal to the cytoplasmic G-protein Trends Pharmacol Sci. 2012 Jan; 33(1): 17-27 GPCR movement upon ligand binding Grey is the unliganded protein, cyan shows conformation upon ligand binding TM6 in β2 AR moves 14 Å – bending at a conserved Pro kink TM5 also typically moves in concert (connected by IL3) This opens up a large cleft for the G-protein to bind The β-Adrenergic Receptor is a GPCR Adrenergic receptors = protein receptors in the plasma membrane that bind epinephrine (adrenalin) – four general types: α1, α2, β1, β2 β-adrenergic receptors = applies to both β1 and β2 subtypes GPCR PDB 2YCW More than a third of all drugs target GPCRs (e.g., “beta blockers” used to treat hypertension, cardiac arrythmias, glaucoma, anxiety, migraines all target the GPCR β-adrenergic receptor)