Receptor Types and Signaling Mechanisms

The exchange of GDP for GTP on the alpha subunit of the G protein, leading to its activation.

A type of receptor that uses a G protein to relay signals within the cell.

A molecule that acts as a messenger inside the cell, relaying signals from the GPCR.

A subunit of the G protein that activates adenylyl cyclase, the enzyme that converts ATP into cAMP.

An enzyme that converts ATP into cAMP, a second messenger involved in various cellular processes.

This toxin binds to the alpha subunit of the G protein and prevents the hydrolysis of GTP, leading to persistent activation of the G protein.

A family of G proteins that inhibit adenylyl cyclase.

This toxin locks the alphai subunit into an inactive configuration, preventing its function.

A type of G protein that activates phospholipase C (PLC) upon binding to its receptor.

A family of metabotropic receptors activated by acetylcholine, playing a crucial role in the autonomic nervous system.

A key enzyme that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG), both important secondary messengers.

A water-soluble second messenger that travels to the endoplasmic reticulum (ER) and triggers the release of calcium.

A lipid-based second messenger that remains in the cell membrane, where it activates protein kinase C (PKC).

A calcium-dependent protein kinase that plays a role in various cellular processes, including cell growth and differentiation.

The process of activating the phospholipase C pathway, which in turn leads to the release of calcium and activation of protein kinase C.

The result of the activation of G proteins containing alphaq11 subunits, leading to the release of intracellular calcium and activation of other signaling pathways.

These receptors contain two guanylyl cyclase domains which convert GTP to cyclic GMP (cGMP). cGMP then activates downstream kinases to trigger cellular responses.

Binding of a ligand, like atrial natriuretic peptide (ANP), induces a conformational change in the receptor, causing it to dimerize and activate. This activates the guanylyl cyclase activity, generating cGMP. The increased cGMP then activates other signaling molecules, determining the cellular response.

cGMP is generated.

ANP signaling via guanylyl cyclase leads to vasodilation, relaxing vascular smooth muscle and dilating blood vessels.

These receptors contain serine-threonine kinase domains that phosphorylate target proteins, similar to protein kinase A (PKA).

First messenger binds to receptor type II, initiating a cascade. Receptor type I then binds to form a ternary complex with type II and the first messenger. Type II receptor phosphorylates type I, activating its serine-threonine kinase activity. The activated type I then phosphorylates target proteins, often SMAD proteins. This pathway plays a role in TGF-β mediated cell proliferation.

These receptors contain tyrosine kinase domains that phosphorylate themselves and other proteins.

Binding of two insulin molecules causes the receptor to dimerize. The receptors then use their cytoplasmic tyrosine kinase activity to phosphorylate each other at multiple tyrosine residues, creating 'phosphotyrosine motifs'.

A second messenger that promotes calcium release from the endoplasmic reticulum (ER) and increases intracellular free Ca2+, ultimately leading to cellular responses.

IP3 binds to its receptor, IP3R (IP3 receptor), located on the membrane of the ER. This binding triggers the release of Ca2+ into the cytosol.

The SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) pump is responsible for transporting Ca2+ back into the ER. It uses ATP as its energy source.

Calmodulin (CaM) is a calcium-binding protein that plays a central role in mediating various intracellular responses triggered by Ca2+. It binds to four Ca2+ ions, forming the Ca2+-CaM complex.

The complex of Ca2+ bound to Calmodulin (Ca2+-CaM) activates various downstream proteins, including PDE (phosphodiesterase) and CaMKs (calmodulin kinases).

CaMKs phosphorylate serine and threonine residues on specific substrate proteins, playing a role in various cellular processes, such as smooth muscle contraction.

DAG (diacylglycerol) is a second messenger that activates specific protein kinases, primarily protein kinase C (PKC). It plays a role in various cellular processes, including cell proliferation, transcription factor activity, and receptor desensitization.

PKCs can amplify the effects of IP3 signaling, enhancing downstream signaling pathways triggered by IP3 and Ca2+. It is also involved in regulating cell shape and transcription factor activity.

A signalling pathway mediated by tyrosine kinase-associated receptors often involving the release of cytokines, like IL-6, in response to inflammation or infection.

Receptors that contain tyrosine phosphatase domains. These enzymes remove phosphate groups from tyrosine residues on target proteins, effectively 'turning off' their activity.

Signal Transduction via RTPs involves a conformational change in the receptor upon ligand binding, activating its tyrosine phosphatase activity. This dephosphorylates target proteins and can trigger phosphorylation of downstream proteins.

The tyrosine phosphatase activity of the receptor removes phosphate groups from tyrosine residues on target proteins, altering their cellular function and activity.

Dephosphorylation of target proteins by RTPs can trigger phosphorylation of downstream proteins, often involved in signalling cascades and cellular processes.

CD45, a receptor tyrosine phosphatase, plays a key role in lymphocyte maturation by binding to its receptor and initiating a signalling cascade.

GPCRs: 7 transmembrane helices, RTKs: 1 transmembrane helix.

GPCRs: No enzymatic activity, activate G proteins. RTKs: Have enzymatic activity, directly phosphorylate target proteins.

An adaptor protein binds to a phosphotyrosine residue on an activated receptor tyrosine kinase (RTK), facilitating the recruitment of RAS-GEF, a crucial intermediary in activating Ras.

RAS-GEF, a guanine nucleotide exchange factor, stimulates Ras to release its bound GDP and bind to GTP, activating Ras.

The activated Ras protein, now bound to GTP, anchors itself to the plasma membrane via a lipid group and initiates the transmission of the signal to downstream pathways.

The first kinase in the MAP kinase cascade (e.g., RAF) is activated by Ras-GTP. It then phosphorylates MAPKK, transferring a phosphate from ATP to ADP.

The second kinase in the MAP kinase cascade, activated by MAPKKK. It phosphorylates MAPK.

The third kinase in the MAP kinase cascade, activated by MAPKK. It translocates to the nucleus to phosphorylate transcription factors, thereby altering gene expression.

These receptors lack intrinsic kinase domains but are associated with cytoplasmic tyrosine kinases, which are non-covalently bound.

Binding of a signaling molecule to the receptor causes a conformational change, leading to dimerization. This dimerization activates the associated tyrosine kinases, such as JAK2. These kinases then phosphorylate tyrosine residues on both themselves and the receptor, creating 'phosphotyrosine motifs.' These motifs recruit intracellular signaling molecules, such as STAT proteins, initiating the cellular response.