ligand binding

drug definition

any chemical which exerts a biological effect upon the body

includes small molecules, natural products, biologics and endogenous chemicals

receptor definition

a protein which binds to a soluble physiological signalling molecule o elicit change in cellular behaviour

types of chemical interactions

covalent bonds

ionic bonds

dipole interactions

hydrogen bonds

van der waals

hydrophobic effects

aromatic interactions

fractional occupancy

proportion of receptors occupied by drug

pharmacological action is directly proportional to number of receptors

efficacy

ability of a drug to activate a receptor which influences cell signalling

spare receptors

not all receptors need to be occupied to produce maximal response

if no spare receptors Kd = EC50

partial agonists

lower maximal response than full agonist

two state model of drug action

agonist stabilises R* conformation

partial agonists stabilise R* less than agonist

antagonist acts in middle of eqm

inverse agonist stabilises R

potency

concentration of a drug required to elicit a given biological effect

combination of affinity and efficacy

orthosteric binding

drug competes with endogenous ligand for binding site

only one drug can bind

allosteric binding

drug binds to distinct site on receptor

alters through conformational change

features of cell signalling pathways

signal amplification

integration

localisation

temporal dynamics

signal bias

redundancy

signal termination

desensitisation

families of ligand gated ion channels

Cys loop

glutamate gated

purine

ligand gated ion channels activation

alters membrane potential

rapid response

selectivity based on size and charge

nuclear receptors activation

ligand activated TFs

class 1 nuclear receptors

cytoplasmic

bound inhibitory complex

steroid ligand diffuses and releases inhibitory complex

homodimerises in nucleus

can recruit other activators

class 2 nuclear receptors

nucleus

thyroid hormones and metabolic ligands

low affinity binding

heterodimerises with RXR

non classical nuclear receptor signalling

found at plasma membrane or in organelles and exert non genomic actions

types of enzyme linked receptors

membrane bound GCs

soluble GCs

RTK

RSK

cytokine receptors

membrane GCs

homodimers

activated by natriuretic peptides or intestinal polypeptides

cGMP affects ion channels and kinases

soluble GCs

heterodimers

heme binding domain and catalytic domain

activated by NO binding to heme binding domain

causes catalytic domain to produce cGMP

cGMP inhibits MLCK

RTKs

single TM domain

extracellular TK domain

dimerise upon ligand binding

autophosphorylation

RSKs

heterodimers

ligand binding causes dimerization

autophosphorylation

SMAD proteins bind

cytokine receptors

closely linked to kinases

JAK/STAT

dimerise upon ligand binding

phosphorylation by associated kinases

GPCR structure

7 TM domains

extracellular N terminus and intracellular C terminus

associate with heterotrimeric G proteins

alpha su binds 3rd cytosolic loop of GPCR

GPCR activation

ligand binding causes GPCR to activate G protein - stabilises association with G alpha

GPCR acts as GEF - GTP form

active G protein dissociates

PKA

2 cAMP bind regulatory domains, releases catalytic subunits

can phosphorylate and activate CREB which activates CREs

AKAP anchors PKA to membrane

biased agonist at mu opioid receptor

oliceridine

side effects activated by beta gamma pathway - preferential to Galpha activity

termination of GPCR signalling

ligand dissociation

ligand degradation

desensitisation

GTPase activity

degradation of second messengers

heterologous desensitisation

in response to second messengers

PKA phosphorylates GPCRs at 3rd cytosolic loop and N terminus

prevents association of G protein

changes specificity to Gi

homologous desensitisation

triggered by agonist binding

GRKs phosphorylate C terminal tail

increases affinity for beta arrestin

mediates clathrin dependent endocytosis

reduces number of receptors at membrane