in nucleus, heterodimers, low affinity
operates as RXR heterodimers
in cytoplasm, homoimers, high affinity
1 transmembrane domain, forms dimers upon ligand binding
0 transmembrane domains, it is in the cytoplasm
7 transmembrane domains, single polypeptide chain of <1100 residues
4 transmembrane domains, 5 subunits, binds 2 ligands

Drug Targets (4)

1) Classical Receptors

I. Ligand Gates Ion Channels

II. GPCRs

a. Rhodopsin Family

b. Secretin/Glucagon Family

c. Metabotropic Glutamate Receptor/ Ca Sensor Family

Isoforms of G protein

G alpha s

Upon ligand binding, 'G alpha s' protein dissociates from complex and GDP-> GTP. Activates AC. AC converts ATP to cAMP which goes on to activate PKA.

G alpha i

Upon ligand binding, 'G alpha I' protein dissociates from complex and GDP -> GTP. The protein then inhibits AC so that no cAMP is produced, and thus PKA remains inactive.

G q

Upon ligand binding, 'G alpha Q' dissociates and GDP-> GTP. Activates Phospholipase which then converts PIP3 (in membrane) to IP3 and DAG. DAG activates PKC which goes on to phosphorylate substrates. IP3 travels across the cytosol to the ER where it binds to Ca2+ channels to allow for the outpour of Ca2+ into the cytosol.

IV. Nuclear Receptors

CLASS 1

Hybrid Class

CLASS 2

III. Kinase-Linked Receptors

RTKs
-receptors for growth factors like EGF, NGF and toll-like receptors

Serine/Threonine Kinases
-Transforming Growth Factor Receptor

Cytokine Receptors
-Associate with JAK

2) Ion Channels

3) Enzymes

4) Transporters