L11 Kinase linked receptors

Question 1

Describe phosphorylation and its impact on target proteins

Answer 1

biochemical process in which a phosphate group is added to a molecule, (protein) by a type of enzyme known as a kinase.

Kinases can activate proteins

Question 2

Name the three amino acids involved in protein phosphorylation

Answer 2

Serine
Threonine
Tyrosine

Question 3

Classify kinase-linked receptors with example(s)

Answer 3

Tyrosine kinase-associated receptors: cytokines
Receptor tyrosine Kinase: Insulin receptor and epidermal growth factor receptor

Question 4

Draw a diagram to illustrate and describe signal transduction mediated by tyrosine kinase-associated receptors

Answer 4

On the slides

• Signal transduction in TKAR happens when binding of ligand (cytokine) to its receptor causes receptor dimerization
• and subsequently, Janus Kinases (JAKs) are activated and phosphorylate tyrosine residues.
• P-tyrosine res are recognised by binding of SH2-domain protein: STAT (signal transducer and activator of transcription) and STAT binds to it and in close proximity to Jak so it is phosphorylated.
• Will dissociate from receptor and dimerise with another P-STAT then translocate to the nucleus for gene transcription

Question 5

Draw a diagram to illustrate and describe signal transduction mediated by receptor tyrosine kinases

Answer 5

*** Has intrinsic activity
**
* Signal transduction in RTK happens when binding of ligand (cytokine) to its receptor causes receptor dimerization
* tyrosine auto-phosphorylation & binding of SH2-domain protein (Grb2-Growth factor receptor bound protein 2)
* Grb2 will be Phos by receptor
* Grb2 will interact with SOS (guanine nucleotide exchange factor)
* will interact with Ras (a GTPase) that is GDP bound until SOS interacts will facilitate exchange to GTP-bound
* Initiate kinase cascade with 3 serine/threonine kinases
* Raf -> Mek -> MAPK upon phosphorylation
* After MAPK phos will translocate to nucleus and Phosphorylate other transcription factors to regulate gene transcription

Question 6

The insulin receptor

Answer 6

(αβ)2 (a dimer of heterodimers)
* extracellular α subunit and intracellular
β subunit are linked by disulfide bonds

Question 7

The insulin receptor unliganded and liganded

Answer 7

• unliganded - access of substrates to the active site is blocked due (site is kinase domain)
  to activation loop inhibition
• liganded - activation loop inhibition removed -> expose binding site and activate loop is phosphorylated and then activate receptor itself.
• phosphorylation of tyrosine in the activation loop

Question 8

Insulin receptor-mediated signaling through

Answer 8

insulin receptor substrate (IRS) dependant →
Grb2/SOS/Ras/Raf/MEK/MAPK → downstream effectors

Question 9

What activated protein kinase A and C

Answer 9

A: cAMP
C: Diacylglycerol

Question 10

Fluoro
Insulin-stimulated translocation of GLUT4

Answer 10

• GLUT 4 - Solo carrier
• How fluorense is used to monitor protiens -> C-terminius has fluoro protein and a extracullular myc tag to see if inserted to membrane
• It is recognised by anti-myc antibodies and use immunofluorescenes to see if on the cell membrane because of recognition
• W/O insullin fluoro protein exposed to cypoplasm and on Glucose transporter 4 vesicles - once they fuse eith the cell membrane the myc is exposed and recognise and detect immunofluoro

Question 11

GLUT 4 translocaton

Answer 11

stimulation of the insulin receptor by insulin will cause the translocation of glucose is transported, and therefore increase the number of glucose supporters at the cell membrane and subsequently increase glucose uptake.
1st: parking bay - where gluc vesicles should be fused to
2nd: guides translocation and facilitate exocyctosis of content to the cell membrane.

Question 12

RTK EGFR

Answer 12

high expression of epidermal growth factor receptor (EGFR) in cancer cells (Activity enhanced in cancer cells mutation makes it active in abscence of ligand so overexpression)
1.ligand binding
2.receptor dimerisation
3.tyrosine (Y) phosphorylation (requires ATP binding)
4.Intracellular signalling
5. effect

Question 13

Small molecule TK inhibitors in EGFR

Answer 13

Small molecule TK inhibitors will prevent ATP binding to pocket -> no substrate phosp - inhibit growth and proliferation of cancer

Question 14

GPCR phosphorylation

Arrestin

Answer 14

• GRK-mediated GPCR phosphorylation blocks G protein-mediated signalling
• the GPCR-arrestin complex serves as a scaffold and facilitates different signalling pathways

Question 15

Drug tolerance is the diminished response to a drug following repeated or prolonged exposure
* change in receptors, e.g.,
* translocation of receptors, e.g.,

Answer 15

1. receptor phosphorylation
2. internalisation of GPCR