Lecture 2 (Receptors as Drug Targets)

Question 1

What is a Ligand?

Answer 1

Ligand refers to any molecule that binds to the receptor,
it may be an agonist or an antagonist

Question 2

What are the 4 receptor families? (4)

Answer 2

Type 1 – Ligand gated ion channels
Type 2 – G protein couple receptors
Type 3 – Kinase linked receptor
Type 4 – Nuclear receptor

Question 3

Describe Ligand gated ion channels in terms of transmembrane proteins and binding site? (2)

Answer 3

-4 Transmembrane protein
-Binding site facing out of cell

Question 4

Describe G-protein coupled receptors in terms of transmembrane proteins, binding site and other features? (3)

Answer 4

-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

Question 5

Describe Kinase linked receptors in terms of transmembrane proteins and binding site? (2)

Answer 5

-1 Transmembrane protein
-Binding domain faces outside of the cell

Question 6

Describe Nuclear receptors in terms of transmembrane proteins and binding site? (2)

Answer 6

-No transmembrane domain not anchored in plasma membrane but found in cytosol or nucleus
-Receptor found within cell

Question 7

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

Answer 7

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

Question 7

What is channel gating controlled by?

Answer 7

Ligand binding

Question 8

Which type of receptor are opioids involved with?

Answer 8

G-protein

Question 9

What are the distinct families of ligand gated ion channels based on molecular architecture and their number of transmembrane domains? (4)

Answer 9

-Cys-loop type (pentameric)
-Ionotropic glutamate type (tetrameric)
-P2X type (trimeric)
-Calcium release type (tetrameric)

Question 10

What is the largest family of transmembrane receptors in humans?

Answer 10

G-protein coupled receptors
(differ by binding site)

Question 11

What are the 3 subunits of the G protein? (3)

Answer 11

-Alpha
-Beta
-Gamma

Question 12

How does canonical/classical signalling by GPCRs work? (6)

Answer 12

-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)

Question 13

What are the two ways to terminate canonical signalling in GPCRs? (2)

Answer 13

-Alpha subunit breaks down GTP to GDP so becomes more attractive to Beta Gamma
-Agonist is no longer around so signalling is terminated

Question 14

What kind of pathways do GPCRs have?

Answer 14

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

Question 15

How can we detect second messenger level of GPCR signals?

Answer 15

We can produce assays to detect them with various robotics

Question 16

How much of the protein-coding capacity of human genome do GPCRs take up?

Answer 16

Over 1%

Question 17

What is the common architecture of GPCRs?

Answer 17

-Common architecture of seven membrane-spanning helices connected by intra- and extracellular loops

Question 18

What do extracellular loops do in GPCRs?

Answer 18

-Extracellular loops contain two highly conserved cysteine residues that form disulphide bonds to stabilize the structure of the receptor

Question 19

What do GPCRs recognise? (5)

Answer 19

Diverse messengers such as light, odorants, small molecules, hormones, and neurotransmitters

Question 20

What do most GPCRs act as?

Answer 20

-Guanine nucleotide exchange factors; activated by ligand binding

-Promote GDP-GTP exchange on associated heterotrimeric guanine nucleotide-binding (G) proteins

Question 21

What are the two models for GPCR G-Protein interaction? (2) and what do they do in turn?

Answer 21

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

Question 22

What physiological functions are GPCRs involved in? (4)

Answer 22

-Visual sense
-Smell
-Behavioural regulation
-Functions of the autonomic nervous system and regulation of the immune system and inflammation

Question 23

What factors are used to divide GPCRs into classes ? (2)

Answer 23

sequence homology and functional similarity

Question 24

What are the GPCR mammalian classes? (3)

Answer 24

-Rhodopsin-like family A
-The Secretin receptor family B
-The Metabotropic glutamate/pheromone receptor family C

Question 25

How many Receptor Tyrosine Kinases (RTKs) - Type 3 do human cells contain and how many subfamilies based on domain architecture? (2)

Answer 25

-Human cells contain ~60 RTKs, grouped into 20 subfamilies based on their domain architecture

Question 26

What are RTK subfamilies categorised by?

Answer 26

Extracellular ligand-binding domain

Question 27

What do RTKs generally associate into?

Answer 27

Dimers

Question 28

How are RTKs activated?

Answer 28

Activated by autophosphorylation on conserved intracellular tyrosine residues

Question 29

What does autophosphorylation do?

Answer 29

Autophosphorylation increases the catalytic efficiency of the receptor and provides binding sites for the assembly of downstream signalling complexes

Question 30

What does activation of signalling pathways on RTKs result in?

Answer 30

Activation of these pathways ultimately results in changes in gene expression and cellular metabolism

Question 31

How many receptors in Type 4 receptors (Nuclear)?

Answer 31

48

Question 32

What do all nuclear receptors contain?

Answer 32

All the nuclear receptors contain a central DBD (region C), which is the most highly conserved domain and includes two zinc finger modules

Question 33

Where Is LBD region E located in type 4 receptors (nuclear)?

Answer 33

A LBD (region E) is contained in the C-terminal half of the receptor

Question 34

What is situated between DBD and LBD in type 4 receptors (nuclear)?

Answer 34

A variable length hinge domain (region D), and variable N-terminal region (A/B) contains ampF-I activation function

Question 35

What do most type 4 receptors (nuclear) contain that has a function which is yet to be understood?

Answer 35

a variable length C-terminal region F

Question 36

What do class 1 receptors act as?

Answer 36

Homodimers that transfer to nucleus

Question 37

What do class 2 receptors detect?

Answer 37

lipids or metabolites