L7: Receptors as drug targets part 2 Flashcards
GPCR
Ligand Binding Site:
The ligand binding site is not sticking out in the extracellular matrix. Instead, it’s located in a pocket within the transmembrane domain of the receptor. This is where the ligands bind.
Intracellular Loop (Red loop):
The red loop refers to the intracellular loop that is involved in coupling the receptor to G proteins. This loop helps the receptor recognize and interact with G proteins to initiate cellular signaling.
Class B Receptors:
For Class B G-protein coupled receptors (GPCRs), the binding site is at the N-terminus because most of the agonists (activating molecules) for these receptors are peptides, which are too large to fit into the typical binding pocket in the transmembrane domain.
Class C Receptors:
Class C GPCRs typically act as dimers (two subunits together). In contrast, Class A GPCRs generally act as monomers (single subunit).
Class C receptors require two subunits to come together to form a functional receptor, and they also have a binding site on the extracellular domain (outward-facing).
Third Intracellular Loop for Coupling:
Despite the differences in how Class A, B, and C receptors function and bind ligands, they all have a third intracellular loop that is crucial for coupling with G proteins. This loop is common across these receptor classes.
Variable Length of N-Terminus:
The N-terminus of these receptors can vary in length across different receptor types, which influences the overall structure and functionality of the receptor.
intrinsic enzyme receptors?
also called plieotropic receptrs- found in all cell types
or catalytic receptors
include receptors for growth factors, cytokines and insulin.
1 or 2 ™ domains and enzyme found intracellularly. Does not require g protein coupling. Ligand binding activates the enzyme. Growth factors, cytokines and insulin receptors.
Intrinsic enzyme receptors (like RTKs) have kinase activity inside the cell.
When the ligand binds to the extracellular domain, it causes the receptor to dimerize (pair up with another receptor).
This dimerization allows the receptors to autophosphorylate (phosphorylate each other).
Once phosphorylated, the receptors can phosphorylate other proteins inside the cell, starting a signaling cascade.
usually known as kinase receptors aswell
DNA binding receptors?
also called: nuclear receptors, ligand activated transcription factors
include receptors for: steroid hormones, thyroid hormones, vitamin d, retinoic acid
Nuclear receptors are often found in the nucleus, but some are also in the cytosol because they need to be activated inside the cell.
They are also called ligand-activated transcription factors.
These receptors don’t rely on ligands outside the cell; the ligand crosses the plasma membrane (PM) and activates the receptor inside the cell.
Zinc fingers are a protein structure with zinc ions that help the receptor bind directly to DNA.
Most of these receptors are activated by??? lipophilic molecules (like fatty acids) that can pass through the plasma membrane.
slide 16 has examples
Receptor not found in pm like first 3 were. Find inside cell and sitting there watiing for ligand to come through membrane. So ligand must be lipohillic to cross membrane. Binds to one of these and requires seocn dbound one for dimerisationa nd allows it to translocate inside nucleus through nuclear pores where it interacts with dna and alters transcription of genes so change protein synthesis inside the cell.
properties of the diff families?
Ion channels- structure of multiple subunits. transmembrane domains so must be in pm. Speed of response is very fast. Around 100 microseconds (micro to ms)Amplification is low. Open channel ions flow through channel closes? About 20 types in the body. Quite selective.
Gpcr: usually single protein but can act as dimers. Fast (ms-s). Sowqmething in eye= 10ms? Amplification is very high. Ligand binding causs activation by gpcr to about 20 proteins that actovate enzymes and can gen many second messangers. Number of types: 1000.
Intrinsic enzyme: often dimers. Relativley slow (mins-hours) quite high amplification. Once actovate phosphorylate or actovate a number of receptors that leads to phosphorylating proteins inside cell? About 10 different types.
Dna binding: very slow. Dimers. Hours-days. Activate then have to wait for protein synthesis? Amplification high.50 diff types.
1 reason why receptors fall into diff subgroups- speed of response
How good at amplification?
Idk if structures and types are involved
G protein?
A multifunctional protein
has an area for receptor binding at C terminus, effector binding and activating at N terminus, CTPase activity, GTP and GDP binding, beta gamma subunit binding
G-proteins are globular (spherical or ball-like) proteins composed of three subunits: alpha (α), beta (β), and gamma (γ).
These proteins do not contain transmembrane domains themselves, but they interact with G-protein-coupled receptors (GPCRs), which do have transmembrane regions.
Function:
The beta-gamma subunits typically help keep the alpha subunit inactive (bound to GDP) on the inner membrane surface. When activated, alpha will exchange GDP for GTP, leading to dissociation of alpha from beta-gamma.
The alpha subunit binds GTP in the active state, and the GTPase activity in the alpha subunit allows it to hydrolyze GTP back to GDP, which inactivates it.
GTP/GDP Binding:
The G-protein cycle involves a switch between GTP-bound (active) and GDP-bound (inactive) states. The GTP binding occurs in a specific region of the alpha subunit.
This cycle is regulated by the G-protein’s intrinsic GTPase activity, converting GTP into GDP. This change of state is critical for signaling.
Activation:
When a receptor (like a GPCR) binds its ligand, the intracellular loops of the receptor interact with the C-terminus of the G-protein. This interaction triggers the exchange of GDP for GTP on the alpha subunit.
The alpha subunit (now GTP-bound) dissociates from the beta-gamma subunits, and both alpha and beta-gamma subunits can activate downstream signaling molecules.
Physiological State:
Under physiological conditions, the beta-gamma subunits are typically bound to the alpha subunit in its inactive, GDP-bound form.
The N-terminus of the G-protein is where the effector protein (a downstream signaling target) binds once the G-protein has been activated.
check if correct based on notes
G protein activation?
G proteins are activated by receptors.
Short N-terminus:
The N-terminus of some receptors is short and often located in the extracellular region, while the ligand binding site is within the transmembrane (TM) domain of the receptor. This allows the receptor to interact with the ligand from the outside of the cell.
Rest State:
In the resting state, the G-protein is not bound to the receptor. The alpha subunit is GDP-bound and also associated with the beta-gamma subunits of the G-protein. No downstream signaling occurs in this state.
Ligand Binding:
Upon ligand binding, the receptor undergoes a conformational change in its 3D structure, opening up a region that allows the third intracellular loop (ICL3) of the receptor to interact with the C-terminus of the alpha subunit of the G-protein.
G-protein Activation:
In the resting state, the alpha subunit is GDP-bound and is also associated with the beta-gamma subunits.
Upon receptor activation, the alpha subunit undergoes a GDP-GTP exchange. When the receptor changes shape, the affinity of the alpha subunit for GDP decreases, and the affinity for GTP increases. This leads to the alpha subunit releasing GDP and binding GTP instead.
Lipidation of Beta-Gamma:
The beta-gamma subunits are often lipidated (attached to lipids), which helps them stay anchored near the plasma membrane (PM) or intracellular membranes. This lipidation allows the beta-gamma complex to stay close to the membrane and facilitates its interaction with membrane-bound proteins.
Interaction of Beta-Gamma and Alpha Subunit:
After the alpha subunit binds GTP, it dissociates from the beta-gamma subunits, and both components can activate downstream signaling pathways.
The alpha subunit is more polar and therefore interacts with cytosolic proteins (signaling molecules) once it has dissociated from the beta-gamma subunits.
check if accurate based on notes
