Lecture 2 (Receptors as Drug Targets) Flashcards
What is a Ligand?
Ligand refers to any molecule that binds to the receptor,
it may be an agonist or an antagonist
What are the 4 receptor families? (4)
Type 1 – Ligand gated ion channels
Type 2 – G protein couple receptors
Type 3 – Kinase linked receptor
Type 4 – Nuclear receptor
Describe Ligand gated ion channels in terms of transmembrane proteins and binding site? (2)
-4 Transmembrane protein
-Binding site facing out of cell
Describe G-protein coupled receptors in terms of transmembrane proteins, binding site and other features? (3)
-7 Transmembrane domains
-Binding site is either exposed to outside or buried a bit down in protein structure
-These receptors have complex long end of protein where G protein attaches
Describe Kinase linked receptors in terms of transmembrane proteins and binding site? (2)
-1 Transmembrane protein
-Binding domain faces outside of the cell
Describe Nuclear receptors in terms of transmembrane proteins and binding site? (2)
-No transmembrane domain not anchored in plasma membrane but found in cytosol or nucleus
-Receptor found within cell
Describe the 4 types of receptor families in terms of speed at which receptors bring change and why (4)?
Type 1 – Ligand gated ion channels
Type 2 – G protein couple receptors
Type 3 – Kinase linked receptor
Type 4 – Nuclear receptor
Type 1 - Ligand gated are fastest type of receptors
Type 2 - G-protein sets up cascade of events so are slower (still extremely fast)
Type 3 - Kinase linked so phosphorylation causes changes in gene transcription, slower in bringing about changes
Type 4 - Nuclear receptors, takes a couple of hours
What is channel gating controlled by?
Ligand binding
Which type of receptor are opioids involved with?
G-protein
What are the distinct families of ligand gated ion channels based on molecular architecture and their number of transmembrane domains? (4)
-Cys-loop type (pentameric)
-Ionotropic glutamate type (tetrameric)
-P2X type (trimeric)
-Calcium release type (tetrameric)
What is the largest family of transmembrane receptors in humans?
G-protein coupled receptors
(differ by binding site)
What are the 3 subunits of the G protein? (3)
-Alpha
-Beta
-Gamma
How does canonical/classical signalling by GPCRs work? (6)
-When agonist binds to receptor motion translated to Alpha subunit
-Makes Alpha subunit less attractive to GDP and not GTP
-GTP associates to Alpha subunit which disassociates it from the Beta Gamma complex
-Beta Gamma can now interact with downstream effector proteins which bring about change in cell
-Alpha subunit Breaks GTP down into GDP and releases one phosphate
-Alpha subunit now associated with GDP so more attractive to Beta Gamma and rejoins (terminates signalling)
What are the two ways to terminate canonical signalling in GPCRs? (2)
-Alpha subunit breaks down GTP to GDP so becomes more attractive to Beta Gamma
-Agonist is no longer around so signalling is terminated
What kind of pathways do GPCRs have?
Signal transduction pathways
Multiple subtypes of G-proteins
Depending which G-protein receptor regulates, impacts what targets in talks to and which secondary messengers it regulates
How can we detect second messenger level of GPCR signals?
We can produce assays to detect them with various robotics
How much of the protein-coding capacity of human genome do GPCRs take up?
Over 1%
What is the common architecture of GPCRs?
-Common architecture of seven membrane-spanning helices connected by intra- and extracellular loops
What do extracellular loops do in GPCRs?
-Extracellular loops contain two highly conserved cysteine residues that form disulphide bonds to stabilize the structure of the receptor
What do GPCRs recognise? (5)
Diverse messengers such as light, odorants, small molecules, hormones, and neurotransmitters
What do most GPCRs act as?
-Guanine nucleotide exchange factors; activated by ligand binding
-Promote GDP-GTP exchange on associated heterotrimeric guanine nucleotide-binding (G) proteins
What are the two models for GPCR G-Protein interaction? (2) and what do they do in turn?
1) ligand-GPCR binding first, then binding to G Proteins
2) “Pre-coupling” of GPCRs and G Proteins before ligand binding
-These in turn activate effector enzymes or ion channels
What physiological functions are GPCRs involved in? (4)
-Visual sense
-Smell
-Behavioural regulation
-Functions of the autonomic nervous system and regulation of the immune system and inflammation
What factors are used to divide GPCRs into classes ? (2)
sequence homology and functional similarity
What are the GPCR mammalian classes? (3)
-Rhodopsin-like family A
-The Secretin receptor family B
-The Metabotropic glutamate/pheromone receptor family C
How many Receptor Tyrosine Kinases (RTKs) - Type 3 do human cells contain and how many subfamilies based on domain architecture? (2)
-Human cells contain ~60 RTKs, grouped into 20 subfamilies based on their domain architecture
What are RTK subfamilies categorised by?
Extracellular ligand-binding domain
What do RTKs generally associate into?
Dimers
How are RTKs activated?
Activated by autophosphorylation on conserved intracellular tyrosine residues
What does autophosphorylation do?
Autophosphorylation increases the catalytic efficiency of the receptor and provides binding sites for the assembly of downstream signalling complexes
What does activation of signalling pathways on RTKs result in?
Activation of these pathways ultimately results in changes in gene expression and cellular metabolism
How many receptors in Type 4 receptors (Nuclear)?
48
What do all nuclear receptors contain?
All the nuclear receptors contain a central DBD (region C), which is the most highly conserved domain and includes two zinc finger modules
Where Is LBD region E located in type 4 receptors (nuclear)?
A LBD (region E) is contained in the C-terminal half of the receptor
What is situated between DBD and LBD in type 4 receptors (nuclear)?
A variable length hinge domain (region D), and variable N-terminal region (A/B) contains ampF-I activation function
What do most type 4 receptors (nuclear) contain that has a function which is yet to be understood?
a variable length C-terminal region F
What do class 1 receptors act as?
Homodimers that transfer to nucleus
What do class 2 receptors detect?
lipids or metabolites
