Matise - Signalling Mechanisms Regulating Cell Communication

Question 1

Major receptor classes (4)

Answer 1

1) Ion channels
2) Steroid hormone receptors
3) Protein kinase receptors
4) 7 alpha helix receptors

Question 2

Ligand-gated ion channels

Answer 2

Ligand binding opens/closes channel, allowing ion flow across membrane. Ton of diseases causing by improper activation/inactivation

• ex: cystic fibrosis caused by loss of functional chlorine channels, mucus buildup
• gain of function mutations = dominant (constant activation, inapropro)

Question 3

Tetrodotoxin

Answer 3

Blocks sodium channels irreversibly, so fatal

Question 4

Nuclear Steroid Hormone Receptors

Answer 4

Ex: estrogen. hormone binding receptor causes receptor to dissociate from a chaperone protein, then complex dimerizes with another receptor-hormone complex. Dimer enters nucleus, binds DNA promoter (response element) to cause gene activation. Overexpressed in cancers, treat with competitive receptor binders (tamoxifen)

Question 5

Protein Kinase receptors

Answer 5

kinase: phosphorylates. Has extra, trans, intramembrane components. Usually found as dimer. Main subtypes: tyrosine kinases, serine/threonine kinases
- Activation of PKR brings subunits together to form dimer. Subunits phosphorylate each other, recruit cytosolic proteins

Question 6

Phosphorylation

Answer 6

reversible by phosphotases. Can turn hydrophobic region–>hydrophilic, changing molecular conformations.

Question 7

Grb (G-protein receptor binding) proteins

Answer 7

bind phosphorylated receptors, contain SH2 domain which recognizes phosphorylated tyrosine

Question 8

SoS (GEF) - Son of Sevenless

Answer 8

Binds Grb, activates small G-proteins like Ras

Question 9

Ras (Rat Sarcoma)

Answer 9

typical small G-protein, ~200 others. Activates transcription factors, through MAPK for example. Oncogenic when mutation prevents GTP hydrolysis, so permanently “on”.

Question 10

GEFS (Guanine nucleotide exchange factors)

Answer 10

Activate G-proteins by exchanging GDP–>GTP (inactive–>active)
-ex: eIF1 requires GEF

Question 11

GAPS - GTPase activating proteins

Answer 11

inactivate proteins by converting GTP–>GDP

Question 12

PKR Signaling Pathway

Answer 12

PRK is activated, phosphorylates Grb. SoS binds Grb’s SH2 domain. SoS acts as GEF for ras, GDP–>GTP. Ras activates further cellular targets until it is inactivated by a GAP, GTP–>GDP

Question 13

MAPK

Answer 13

mitogen activated protein kinase. Activates transcription factors following phosphorylation cascade caused by Ras, one of many activated by Ras.

Question 14

Neurofibromatosis Type I

Answer 14

Mutation in gene for Ras GAP causes overactive Ras.

Question 15

Noonan Syndrome

Answer 15

Mutation coding SHP2 causes overactive Ras

Question 16

7 - Helix Receptors

Answer 16

Named for 7 alpha-helix structure, most abundant receptor. Coupled to 3-part G-proteins, A, B, G. Ligand binding causes A phosphorylation, separation of subunits, activation of stuff downstream

Question 17

G-protein alpha subunit types (3)

Answer 17

1) Gs-alpha: phosphorylate PKA (activates adenyl cyclase)
2) Gi-alpha: hydrolyzes PKA (inactivates adenyl cyclase)
3) Gq-alpha: activates PLC, phospholipase C

Question 18

7 alpha helix receptor desensitization (B-adrenergic receptor ex)

Answer 18

B-adrenergic receptor is activated by epinephrine. Receptor + ligand complex is substrate for BARK, B-adrenergic receptor kinase. Phosphorylation by BARK causes B-arrestin to bind. This prevents Gs from binding, preventing activity even with epinephrine present.

Question 19

Gs-alpha /Gi-alpha calcium regulation

Answer 19

Gs activates adenyl cyclase–>cAMP–>PKA–>Ca2+ release. Gi deactivates adenyl cyclase, cutting off Ca2+ release.

Question 20

Gq-alpha calcium regulation

Answer 20

Gq activates Phospholipase C (PLC) –> PiP2 –> DAG + IP3. IP3–>Ca2+ release, Ca2+ + IP3 activate PKC (protein kinase C)

Question 21

Protein Kinase C (PKC) Activation

Answer 21

PKC has two binding domains required for kinase activation, self-blocked by its C1 and C2 domains when inactive. DAG binds one, Ca2+ allows the other to be bound by PS (phosphatidyl serine), activating PKC

Question 22

Calmodulin

Answer 22

Binds calcium to become activated (4 subunits each bind). Activates CAMK, calmodulin-activated protein kinase.

Question 23

CAMK Activation

Answer 23

Like PKC, CAMK is inactive when its subunit blocks active site. Ca2+ - bound calmodulin binds inhibitory domain of CAMK, making active site accessible.
-CAMK key to AD, musculoskeletal disorders, cancer

Question 24

Agonists vs. Antagonists

Answer 24

Agonists: activate receptor pathways (activators)

Antagonists: inactivate receptor pathways (repressors)