Lecture 2: Hormones Receptors and Rhythms

what does the fate of a cell depend on

depends on a multitude of extracellular signals

what are the different responses of cells to signals?

1. survive

2. divide

3. differentiate

what happens if a cell receives NO signals

apoptosis

explain when signal binds to receptor

1. the receptor will recognize the signal

2. change in intracellular network of proteins

3. activate of target gene/ protein

4. cellular response

what are examples of possible target proteins in a cell

metabolic enzyme—> altered metabolism

gene regulatory protein—> altered gene expression

cytoskeletal protein—> alter shape or movement

what is the function of signal mediators?

amplify signal during transmission

what is the definition of cellular response?

cell that has been stimulated by process of cell transduction

explain the whole transmission/transduction pathway

look at drawimg

what are the two different classes of signal receptors

Based on THEIR LOCATIONS

1. cell surface receptors

2. intracellular receptors

explain cell surface receptors

hydrophilic signal molecule binds to cell surface receptor

explain intracellular receptors

small hydrophobic signal molecule—> need a carrier protein

intracellular found in nucleus receptor

explain receptor types of hydrophilic vs hydrophobic hormones

hydrophilic—> cell surface

hydrophobic—> intracellular

what are examples of hormones that have cell surface receptors

prostaglandins and leukotrienes—> BOTH are hydrophobic which is an expection to the general trend

what are the receptors for steroids and bile acids

cell surface and intracellular

can chemical signals be nutrients/metabolites? + how can they be signalling molecules

YES ---> can be signalling molecules as they have receptors

what are the different metabolites that can act as signalling molecules?

1. lactate
2. ketone bodies (BHB)
3. succinate
4. alpha - ketoglutarate
5. fatty acids
6. calcium
7. bile acids

what are the 3 main domains of a cell surface receptor and their locations

1. ectodomain

2. hydrophobic transmembrane domain

3. cytoplasmic domain

what does a signal first bind to

ectodomain

explain the structure of the ectodomain

rich with cysteine residues—> this will have S-S bonds for folding and is needed for conformational changes

also is glycosylated—→ AA are attached to carbohydrate moieties which signals can attach to

do free ectodomains have functions and with example

YES! they can circulate as hormone-binding proteins

EX: the GH receptor's ectodomain acts as a GH binding protein - serves as a carrier protein

what happens if ectodomain is cleaved?

can cause endocrine disease

what is the role of the cytoplasmic domain

relays the signal by inducing a signaling cascade ( relay of conformational chnages of signaling proteins)

what are conformational changes induced by in cytoplasmic domain

1. phosphorylation of proteins

2. binding between proteins

how are signaling proteins mainly modulated by

phosphorylation

what amino acids are most commonly phosphorylated

Serine

threonine

tyrosine

—> all have free OH group that can phosphorylated by KINASES

explain how phosphorylation happens

look at notes

P1—> activated P1 by protein kinases

P1 can then activate P2

remove phosphate by protein phosphatase

what enzymes can reverse phosphorylation

phosphatase

what are the 2 things that are needed to power phosphorylation?

1. protein kinase
2. ATP ---> where the phosphate comes from

how does each phosphorylation step allow for signal amplification?

there is a lag period between being activated + deactivated that allows for signal amplification

which aa are the commonly phosphorylated?

serine and threonine more abundant than tyrosine

when does tyrosine phosphorylation usually occur?

occurs at the beginning of a the cascade bc many first receptors have induce tyrosine kinase activity

what does the phosphorylated tyrosine serve as

serve as a docking site for downstream signal proteins

means that it creates a structure that allows for other proteins to come + sit

what amino acid sequence mediates the docking to phosphorylated tyrosine?

SH2 and SH3 domains is conserved and diagnostic for proteins involved in the signaling cascade

what are the types of cell surface receptors

1. GPCR

2. RTK—> intrinsic and recruited

3. Serine-threonine kinase receptors ( RSTK)

Explain the GPCR pathway

1. the first messenger ( SIGNAL) will bind to receptor

2. binding will activate G protein and the alpha subunit will be shuttled to activate adenylyl cyclase

3. adenylyl cyclase will convert ATP to cAMP

4. cAMP will activate PKa

5. PKa will phosphorylate inactive protein—> will become active

6. active protein can bring about cellular response

what does adenylyl cyclase do?

ATP to cAMP

what is the structure of PKA

exists as a dimer

composed of: PKA c, PKA r, AKAP

what is PKA c

catalyze phosphorylation

what is PKA R

regulates PKA

how many cAMP is needed to activate PKA complex

4 cAMP—> means for 4 ATPs

explain PKA activation

1. cAMP binds to the regulatory subunits of PKA.

2. The catalytic subunits are released.

3. The catalytic subunits phosphorylate target proteins.

what cellular proteins are regulated by cAMP and PKA

what is the second activation of target of GPCR and IP3

phospholipase C

Explain GPCR signaling through IP3 and Ca

1. signal binds to receptor

2. G protein is activated

3. alpha subunit shuttles and activates phospholipase C

4. phospholipase C converts PIP2 to IP3 and DAG

5. IP3 mobilizes intracellular Ca2+

6. Ca2+ acts as SECOND MESSENGER

7. Ca2+ activates calmodulin

8. calmodulin complex activates CaM kinase

9. CaM kinase activates target protein

10. cellular response

what does phospholipase C do

converts PIP2—> IP3 and DAG

what is the fate of DAG

1. DAG activates PKC

2. acts on specific protein

3. cellular response

what is the pathway of signal control desensitization-resensitization cycle of GPCR?

1. epinephrine binds to beta-adrenergic receptor triggers dissociation of Gsby from Gsalpha

2. Gsby recruits bARK to membrane where it phosphorylates Ser residues at carboxyl terminus of receptor

3. b-arrestin (barr) binds to phosphorylated carboxyl terminal domain of receptor

4. receptor arresetin complex enters the cell by endocytosis

5. dissociates and returns to cell surface

what experiment did they perform to learn that for BARR to be recruited NEED a cytoplasmic domain?

had 2 cells ---> 1 w normal cytoplasmic domain thath allowed Barr to b recruited and 1 w/o cytoplasmic domain

in the TRH receptor added rhodamine fluorescent molecule to be able to see it and added green fluorescent protein to BARR

SAW: first cells that had a cytoplasmic domain glowed bc of the florescent dye on BARR
- second cells did not light up

what are five ways target cells can become desensitized to a signal molecule?

1. receptor sequestration ---> moved away from the surface + recycled back
2. receptor down - regulation ---> once internalized it is degraded
3. receptor inactivation
4. inactivation of signalling protein
5. production of inhibitory protein ---> negative regulator is induced

What does Gs alpha do?

activates adenylate cyclase

S = stimualtory

what does Gi alpha do?

inhibits adenylate cyclase

I = inhibitory

what is the role of Gq alpha?

activates phospholipase C

what is the role of Go alpha?

activates ion channels

what is the role of G12/13 alpha?

regulates actin cytoskeleton

can hormones use more than one g protein

YES

the receptors have specfic alpha subunit that will have the specific response