Transmembrane receptors integral membrane proteinsspan the plasma membrane and allow cells to detect and respond to external signals . They function by binding extracellular ligands (such as hormones, growth factors, or neurotransmitters) and triggering a conformational change that initiates intracellular signaling cascades .
Structure: Transmembrane receptors typically have three main regions:
Extracellular domain – Binds the external ligand .Transmembrane domain – A hydrophobic region that anchors the receptor within the lipid bilayer.Intracellular (cytoplasmic) domain – Initiates signaling pathways inside the cell .Main Classes of Transmembrane Receptors: Type Description Example G protein -coupled receptors (GPCRs) 7-transmembrane receptors that activate G proteins β-adrenergic receptor Receptor tyrosine kinases (RTKs) Have intrinsic enzymatic activity (tyrosine phosphorylation ) Epidermal Growth Factor Receptor (EGFR) Ion channel-linked receptors Open or close in response to ligand binding Nicotinic acetylcholine receptor Integrins Bind ECM proteins, link to cytoskeleton , and signal α5β1 integrin binding fibronectin Toll-like receptors (TLRs) Recognize pathogen-associated molecules in immunity TLR4 recognizing bacterial LPS
How They Work (General Mechanism): Ligand binds to the extracellular domain.This causes a conformational change in the receptor. The intracellular domain is either:Directly activated (e.g., via phosphorylation),Or recruits intracellular signaling molecules . This leads to signal transduction , affecting processes like gene expression, metabolism , or cytoskeletal organization. Functions of Transmembrane Receptors: Function Description Signal transduction Relay external signals into the cell to coordinate responses Cell communication Enable interaction between cells and their environment Cell adhesion Some (like integrins) also mediate physical attachment to other cells or the ECM Growth and differentiation Control key decisions in development and tissue maintenance
Clinical Relevance: Cancer Autoimmune diseases Infectious disease : Viruses (e.g., SARS-CoV-2) use transmembrane proteins (like ACE2) as entry points.Drug targets : Over 50% of modern drugs target GPCRs or other transmembrane receptors.Summary Table: Feature Description Location Spans the plasma membrane Key Parts Extracellular domain, transmembrane domain, intracellular domain Binds To External ligands (hormones, neurotransmitters, ECM molecules)Function Converts extracellular signals into intracellular responses Examples GPCRs, RTKs, ion channels, integrins, TLRs Medical Importance Involved in diseases like cancer, infections, autoimmunity, neurological disorders
