Lecture 9- GPCRs structure and function

Question 1

List some key structural features of GPCRs

Answer 1

1. 7TMs which are packed on a similar way
2. TM3 is located next to binding pocket and is crucial for transduction of ligand binding
3. Diversity within the ligand binding pocket- allows them to detect a variety of stimuli
4. N terminal domains vary in size and have different functions
5. C terminal domain vary in length and important for site regulation and protein-protein interactions

Question 2

What type of receptors are PAR receptors and how are they activated?

Answer 2

PAR receptors are GPCRs and activated by proteinases

Question 3

How do thrombin and PAR receptors contribute to blood clot formation?

Answer 3

1. PAR is activated in response to thrombin
2. Thrombin cleaves the N terminal of the PAR receptor which releases a ligand
3. This ligand then binds back onto itself to activate the receptors

Question 4

Outline the basic principles of GPCR signalling

Answer 4

1. Resting/three inactive components
2. Activation of the ligand binding and exchange of GDP for GTP
3. Three separate active components

Question 5

What’s the difference between monomeric and heterotrimeric g-proteins?

Answer 5

• Monomeric: the inactive protein is locked in a GDP bound state. Association with GEF indices a conformational change that allows GDP to come off and be replaced by GTP
• Trimeric: agonist bound receptors act like GEF promoting GDP to GTP exchange

Question 6

What are the key points in receptor signalling?

Answer 6

1. Recognise stimulus
2. Transfer stimulus into cell and amplification of cytoplasmic signal
3. Modulation of effector systems over time
4. Adaptation of system through feedback

Question 7

What regulates the duration of signalling that is activated by trimeric g-proteins?

Answer 7

Regulated by rate of GDP hydrolysis by Ga (alpha)

Question 8

What determines the local concentration of second messengers?

Answer 8

1. Rate of production
2. Rate of diffusion from site of production
3. Rate of removal

Question 9

List structural features of adenylate cyclase

Answer 9

1. 10 isoforms
2. 12 TM domains
3. Membrane anchored enzyme
4. Activated by G(alphas)s and inhibited by G(alpha)i
5. Can have short or long effects

Question 10

List 2 facts about the production of glucose-6 phosphate

Answer 10

1. 5 stages of amplification
2. 7 step pathway

DETAILS FOR BOTH IN LECTURE NOTES

Question 11

How is signalling switched off in the production of glucose-6 phosphate?

Answer 11

1. Agonist dissociating from receptor
2. GTPase activity of G(alpha)s
3. cAMP breakdown of phosphodiesterase
4. Dephosphorylation of enzymes
5. Negative feedback via PKA, B-arrestin and GRK

Question 12

What disease can be caused by an activating and loss of function GPCR mutation?

Answer 12

Activating- hyperthyroidism

Loss of function- hypothyroidism

Question 13

What disease can be caused by excess or deficient GPCR signalling?

Answer 13

Excess- cholera

Deficient- whooping cough