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#transmembrane protein

2 public questions tagged with this topic.

Plasma Membrane Proteins

Which transmembrane protein is a seven-pass receptor involved in signal transduction?

Seven-transmembrane receptor family also termed heptahelical receptors or G protein-coupled receptors comprises largest receptor superfamily in human genome over eight hundred members including rhodopsin-like class A, secretin class B and glutamate class C. Architecture consists of extracellular N-terminal domain ligand binding, seven hydrophobic alpha-helices TM1 through TM7 each nineteen to twenty seven residues traversing membrane with three extracellular loops ECL1-3 and three intracellular loops ICL1-3 and intracellular helix eight parallel to membrane interacting with heterotrimeric G proteins alpha beta gamma. Agonist binding in orthosteric pocket between helices induces conformational change outward movement of transmembrane helix six about six angstroms opening cavity accommodating C-terminal alpha five helix of G-alpha triggering GDP release GTP binding dissociation of beta gamma dimer activating adenylyl cyclase generating cAMP, phospholipase C beta generating inositol trisphosphate and diacylglycerol calcium mobilization, RhoGEFs activating cytoskeleton. Band 3 anion transporter, aquaporin water channel tetramer, spectrin filamentous cytoskeletal spectrin repeat protein contrast with seven-pass signaling architecture.

Ref: Rosenbaum et al., The Structure and Function of GPCRs, Nature 2009.

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Plasma Membrane Proteins

Which of the following interactions primarily stabilizes transmembrane proteins within the lipid bilayer?

Stabilization of transmembrane segments inside bilayer originates from hydrophobic effect plus van der Waals packing. Sec61 translocon provides aqueous pore laterally gated allowing nascent hydrophobic sequence to partition directly into lipid phase assessed by apparent free energy scale of Hessa and von Heijne measuring contribution per residue leucine minus zero point five six kilocalories, arginine positive two point five kilocalories. Burying non-polar side chains of leucine isoleucine valine phenylalanine methionine avoids forcing water to form ordered clathrate cages around them, releasing water to bulk increasing system entropy and providing favorable free energy. Once inserted, side chain interactions with surrounding acyl chains and annular shell lipids contribute additional stabilization minimizing hydrophobic mismatch where thickness adjusts locally via stretching or tilting. Flanking tryptophan tyrosine favor interfacial region aromatic belt via snorkeling, positively charged lysine arginine anchor cytosolic side following positive-inside rule. Ionic hydrogen bonding stabilizes extramembranous loops but not core insertion, covalent lipid anchors define separate class. Hydrophobic interactions therefore dominate stabilization.

Ref: White and von Heijne, How Translocons Select Transmembrane Helices, Annu Rev Biophys 2008.

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