Name: gpcr signaling through g proteins
Uploaded: 2026-08-26T08:19:11.720Z
Duration: 1 min 27 s
Channel: JoVE
Description: G-protein coupled receptors, or GPCRs, start cell signaling after a ligand binds to the receptor. The receptor is a single polypeptide that crosses the cell membrane seven times. These membrane loops create an outside pocket that fits a specific ligand, such as a neurotransmitter or hormone. The inside loops connect to a G-protein.

G-protein-coupled receptors, or GPCRs, are membrane proteins with seven transmembrane alpha helices.The extracellular region of the receptor contains a ligand-binding site that recognizes a wide range of signaling molecules. The intracellular region is coupled to a G protein made up of alpha, beta, and gamma subunits.When a ligand binds to the receptor, the receptor changes shape. This activates the G protein by releasing GDP from the alpha subunit, allowing GTP to bind in its place. The alpha-GTP subunit then separates from the beta-gamma dimer.Both signaling units can now move along the inner surface of the membrane and interact with effector proteins. These interactions trigger intracellular signaling cascades that amplify the signal and direct the cellular response.To stop the signal, the alpha subunit hydrolyzes GTP into GDP. The alpha, beta, and gamma subunits then come back together to form the inactive G-protein, leaving the GPCR ready to respond to another signal.

g protein-coupled receptors

G Protein-coupled Receptors

G-protein-coupled receptors are ligand-binding receptors that indirectly affect changes in the cell. The actual receptor is a single polypeptide that traverses the cell membrane seven times, creating intracellular and extracellular loops. The extracellular loops create a ligand-specific pocket which binds to neurotransmitters or hormones. The intracellular loops hold onto the G-protein.The G-protein, or guanine nucleotide-binding protein, is a large heterotrimeric complex. Its three subunits are labeled alpha (&#x3B1;), beta (&#x3B2;), and gamma (&#x3B3;). When the receptor is unbound or resting, the &#x3B1;-subunit binds a guanosine diphosphate molecule or GDP, and all three subunits are attached to the receptor.When a ligand binds the receptor, the &#x3B1;-subunit releases the GDP and binds a molecule of guanosine triphosphate (GTP). This action releases the &#x3B1;-GTP complex and the &#x3B2;-&#x3B3; complex from the receptor. The &#x3B1;-GTP can move along the membrane to activate second messenger pathways such as cAMP. However, there are different types of &#x3B1;-subunits, and some are inhibitory, turning off cAMP.The &#x3B2;-&#x3B3; complex may interact with potassium ion channels, which release potassium (K+) into the extracellular space, resulting in hyperpolarization of the cell membrane. This type of G-protein-regulated ion channel is called a G-protein-coupled inwardly rectifying potassium channel or GIRK.Ligands do not permanently bind the receptor. When the ligand leaves the receptor, it becomes available for the G-protein units to recouple and reattach. Before this, though, the &#x3B1;-subunit must hydrolyze the GTP back into GDP. Once this is achieved, the &#x3B2;-&#x3B3; complex reassembles with the GDP-&#x3B1; complex, and the whole G-protein reattaches to its receptor domain.Common G-protein coupled receptors are: muscarinic acetylcholine receptors found in smooth and cardiac muscles, Beta-1 adrenergic receptors in the heart, and vasopressin receptors on smooth muscle cells. In sensory systems, like olfactory receptors and some taste receptors, the binding ligands are environmental molecules. For example, sucrose molecules bind G-protein-coupled receptors, resulting in the perception of sweet taste.Alterations in G-protein-coupled receptors may play a substantial role in mood disorders, like depression. Serotonin is a ligand for the 5HT1A receptor, a G-protein-coupled receptor. It has been suggested that, in depression, interactions between the ligand and the receptor are changed; either the ligand does not bind long enough, or the receptor does not fully respond. This results in poor serotonergic signaling, which may contribute to depression.

G-protein coupled receptors are ligand binding receptors that indirectly affect changes in the cell. The actual receptor is a single polypeptide that ...

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Cell Signaling

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gpcr signaling through g proteins

G-protein coupled receptors, or GPCRs, start cell signaling after a ligand binds to the receptor. The receptor is a single polypeptide that crosses the cell membrane seven times. These membrane loops create an outside pocket that fits a specific ligand, such as a neurotransmitter or hormone. The inside loops connect to a G-protein.

GPCR Signaling Through G Proteins

what is cell signaling?

How Cells Send and Receive Signals

Cell signaling lets cells send and receive messages from the environment and from other cells. Even with a protective membrane, cells need to detect changes and respond to them. Unicellular and multicellular organisms use signaling to stay coordinated and to react to outside cues. Cells often rely on receptor proteins in the membrane to sense information. Skin cells can respond to touch, and photoreceptors in the retina can detect light. Most cells respond to chemical signals such as hormones,...

internal receptors

Steroid Hormones and Intracellular Receptors

Steroid hormones and other small signaling molecules can pass through the cell membrane and bind to intracellular receptors inside the cell. These receptors are also called internal receptors. Many hydrophilic signals cannot cross the plasma membrane, so this pathway is used by signals that are small or hydrophobic. Nitric oxide, or NO, also uses this type of signaling. When a ligand, which is a signaling molecule, binds to a receptor in the cytoplasm or nucleus, the receptor changes shape.

contact-dependent cell communication

Cell-to-Cell Signaling via Channels

Cell-to-cell signaling can happen when neighboring cells are in direct contact. In this kind of communication, cells use receptor-ligand interactions or special cytoplasmic channels to move small molecules between them. In animal cells, these channels are called gap junctions. They form when six proteins called connexins assemble into a cylindrical structure in the plasma membrane called a connexon. When connexons from two adjacent cells line up, a channel opens between the cells. Enzymes help...

autocrine signaling

Self-Signaling Cells in Immunity and Cancer

Autocrine signaling is a cell communication method in which a cell sends a signal to itself. The same cell releases an extracellular signaling molecule and also has receptors that can bind to that molecule. This lets the cell respond to its own message. In the immune system, this process is important for homeostasis, or keeping body conditions stable. A well-studied example is the macrophage, an immune cell that secretes cytokines such as interleukin-1, or IL-1. Macrophages also have membrane...

paracrine signaling

Local Cell Signaling in Blood and Healing

Local cell signaling helps cells communicate with nearby neighbors using released signaling molecules. These molecules act only over a short distance because they break down quickly or are inactivated if they are not taken up. This type of signaling supports processes such as nitric oxide signaling in blood vessels, neuron-to-neuron communication at synapses, blood clotting, tissue repair, and local allergic skin reactions. A clear example is nitric oxide signaling in blood vessels. The...

synaptic signaling

Chemical and Electrical Synapses

Neurons send signals across synapses, which are junctions between cells. These signals can excite or inhibit other neurons or target cells such as muscles. Most synapses are chemical. Some are electrical. Chemical synapses use action potentials, which are electrical impulses, to trigger the release of neurotransmitters. The sending neuron is the presynaptic neuron, and the receiving neuron is the postsynaptic neuron. An action potential travels along the axon and reaches the axon terminal,...

endocrine signaling

Hormones Travel to Distant Target Cells

Endocrine signaling uses hormones to send messages to target cells in other organs. Endocrine cells release these hormones into the circulatory system, which carries the signal through the body. Because the hormone reaches the whole organism, only cells with the right receptors respond. This kind of signaling usually acts slowly, but its effects last longer. Endocrine cells can use cell surface receptors or intracellular receptors, depending on the hormone. Cell surface receptors are...

bacterial signaling

Quorum Sensing in Bacteria

Quorum sensing lets bacteria coordinate behavior by sensing how many cells are nearby. Bacteria can signal inside the cell or between cells. When many bacteria act together, they can behave like a community and change gene expression as a group. This signaling starts with autoinducers, or AIs. Individual bacteria make AIs and release them across the cell membrane into the surrounding space. Some AIs diffuse out passively along a concentration gradient, while others are moved out by active...

yeast signaling

Yeast Cell Communication in Mating

Yeast cell communication helps control mating, colony growth, and other cell responses. Yeasts are single-celled organisms, but unlike bacteria, they are eukaryotes with a nucleus. Their signaling works much like cell signaling in other eukaryotic cells. A signal often begins when a ligand, such as a protein or small molecule released from a yeast cell, binds to a receptor on the cell surface. This binding activates second-messenger kinases, which then switch transcription factors on or off.

G-protein coupled receptors, or GPCRs, start cell signaling after a ligand binds to the receptor. The receptor is a single polypeptide that crosses the cell membrane seven times. These membrane loops create an outside pocket that fits a specific ligand, such as a neurotransmitter or hormone. The inside loops connect to a G-protein.

enzyme-linked receptors

Trk Receptors in Cell Signaling

Trk receptors are enzyme-linked receptors that help cells respond to growth factors and some hormones. They belong to the receptor tyrosine kinase, or RTK, family. These receptors can trigger several signals inside a cell after they are activated. Neurotrophin receptors are one RTK group and include TrkA, TrkB, and TrkC, which are tropomyosin-related kinase receptors. TrkA binds nerve growth factor, neurotrophin-6, and neurotrophin-7. TrkB binds brain-derived neurotrophic factor, or BDNF, and...

ion channels

Ion Channels in Cells and Membranes

Ion channels are membrane proteins that help cells move ions across the plasma membrane. Ions such as sodium, potassium, and calcium move into and out of cells to maintain the electrochemical gradient. This gradient supports cell size and volume, nerve signaling, and gas and nutrient exchange. Ion channels are specialized integral membrane proteins that let specific ions pass down their electrochemical gradient. Their main job is to help keep the membrane potential, which is needed for cell...

what are second messengers?

Cell Signals That Use Second Messengers

Cell signals often use second messengers to carry messages inside the cell. Many receptor-binding ligands are hydrophilic, so they do not cross the cell membrane. Instead, the signal is relayed to an internal messenger that can spread the message farther. G-protein coupled receptors can activate the phosphoinositol pathway and the cyclic AMP, or cAMP, pathway. In the phosphoinositol pathway, the receptor activates phospholipase C. This enzyme hydrolyzes phosphatidylinositol biphosphate, or...

intracellular signaling cascades

Cell-Surface Receptor Signal Cascades

Cell-surface receptor signal cascades move information from outside the cell into the cytoplasm. This process is called signal transduction. It happens only with cell-surface receptors, because they cannot interact with most cell parts, such as DNA. Internal receptors are different. They can interact directly with DNA in the nucleus and help start protein synthesis. When a ligand binds to a receptor, the receptor changes shape. That shape change affects the receptor’s intracellular domain or...

key terms and concepts

Learn how G-protein coupled receptors relay signals after ligand binding, from GTP switching and cAMP to GIRK channels, taste, and depression.

GPCR Signaling Through G Proteins | JoVE K12

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GPCR Signaling Through G Proteins

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