Lecture 8: Hormone Receptors Flashcards
What are the 7 domains of a nuclear hormone receptor?
- Hormone binding
- DNA binding
- Nuclear localization
- Dimerization/Modulation/Phosphorylation domains
- Transducing domain
What are the 6 domains of a membrane hormone receptor? Which ones are in the cell and which ones are out?
- Hormone binding (out)
- Transmembrane (within)
- Dimerization (out)
- Modulation (in)
- Phosphorylation (in)
- Transducing domain (in)
What are the 4 ways for a membrane hormone receptor to trigger a second messenger system?
- Dimerization
- Modulation
- Phosphorylation domains
- Enzymatic activity
What method is used by membrane receptors to induce a conformational change leading to transduction of response/second messenger cascade?
Dimerization
Which is inside the cell: N or C terminus of membrane hormone receptor?
Depends!
Where is the hormone-binding domain of nuclear hormone receptors? What is particular about it?
At the C-terminal
LARGE: ~250 AAs
What is the function of the nuclear localization domain of the nuclear hormone receptor?
Allows receptor to localize the nucleus of the cell
When does the nuclear hormone receptor enter the nucleus?
Could have always been there or upon binding to the hormone in the cytosol
What is the transducing domain of the nuclear hormone receptor?
Could be considered the entire hormone receptor
What is an agonist?
Molecule that binds to the hormone receptor and brings about a response
What is an antagonist?
Molecule that binds to the hormone receptor and inhibits the agonist responses
What is the role of the transducing domain of the membrane hormone receptor? What part of the receptor is it?
To induce second messengers
Cytoplasmic side of the receptor
What is the role of the transducing domain of the nuclear hormone receptor?
Activate transcription
Which bind better: agonists or antigonists?
Agonists usually
How can one determine if the binding domain of a hormone receptor binds the hormone reversibly?
Binding assay: scatchard plots
Which type of receptors can be glycosylated?
Membrane receptors
Which type of membrane receptors can have enzymatic activity??
Membrane receptors
What is an example of a partial/weak antagonist?
Ru486: works to inhibit progesterone receptor but partially inhibits the glucocorticoid receptor
What can an antagonist’s properties depend on? Example?
The tissue it is in!
Eg: tamoxifen inhibits estradiol receptors well in breasts and poorly in bone
What does hGR stand for?
Glucocorticoid receptor
What does hMR stand for?
Mineralcorticoid receptor
What does hAR stand for?
Androgen receptor
What does hPR stand for?
Progesterone receptor
What does hERalpha and B stand for?
Alpha and beta estrogen receptors
What does hTR stand for?
Thyroid receptor
What are the 2 main types of hTRs?
Alpha 1 and beta 1
What does hRAR stand for?
Retinoic acid receptor
What are the 3 types of hRARs?
Alpha, beta, gamma
What does hRXR stand for?
Retinoic acid X receptor
What are the 3 types of hRXRs?
Alpha, beta, gamma
What does hPPAR stand for?
Perioxosime proliferator
What do hPPARs regulate?
Lipid metabolism
What are the 3 types of hPPARs?
Alpha, beta, gamma
What does hVDR stand for?
Vitamin D receptor
What are the 3 groupings of nuclear receptors? What do they each share?
- Steroid receptors: hGR, hMR, hAR, hPR
- Estrogen receptors: hER alpha and beta
- Others: hTR (alpha 1 and beta 1), hRAR alpha, hRXR alpha, hPPAR alpha, hVDR
They share P-box sequences
What % range AA homology between the hormone binding domains of nuclear receptors? But…?
15-50%
But conserved structure between all of them.
Describe the common structure of hormone binding domains of nuclear receptors? How come they all have it?
11-12 alpha helices arranged like a 3 layer sandwich with a hydrophobic hole/pocket
Helix 12 is the last helix at the C-terminus with 2 surfaces and is separate from the sandwich: hydrophobic (toward hormone) and hydrophilic –> the hydrophilic one interacts with coactivator proteins to regulate transcription
Evolution!
Describe the mechanism by which nuclear receptors bind hormones.
- Hormone binds and causes all of the helices to crunch together: huge conformational change = induced fit
- Helix 12 seals the binding cavity and exposes its hydrophilic surface to regulate transcription
What is the N terminal of nuclear hormone receptors often involved with?
Transcriptional activation and nuclear localization
Describe the structure of the DNA binding domain of nuclear hormone receptors. Where is it located?
2 zinc fingers + 2 alpha helices in a globular structure
Located in the center of the molecule
What part of the DNA binding domain of nuclear hormone receptors interacts with the DNA? 3 names
The first zinc finger = P-box = recognition helix
How would changing the P-box sequence affect binding of nuclear hormone receptor to DNA?
Would change the binding specificity
Can the hormones activating the nuclear receptors that have the same P-box activate all of them?
NOPE, more complicated than that BUT they could bind to the same DNA binding site
How do ALL hormones bind to nuclear receptors?
As DIMERS to DOUBLE-STRANDED DNA
What DNA sequence do steroid receptors bind?
Palindrome sequence separated by any 3 nucleotides
What DNA sequence do estrogen receptors bind?
Palindrome sequence separated by any 3 nucleotides
What 2 DNA sequences do thyroid receptors bind?
- Palindrome sequence not separated by nucleotides
2. Direct repeats separated by any 4 nucleotides
What DNA sequence do VDRs bind?
Direct repeat separated by any 3 nucleotides
What DNA sequence do RARs bind?
Direct repeat separated by any 5 nucleotides
Which DNA sequences bind nuclear hormone receptors more tightly and with high affitiny: direct repeats or palindromes?
Palindromes
How is steroid receptor binding to DNA regulated?
Heat Shock Proteins are bound to the hormone binding domain of the receptor and are released upon hormone binding
What is the main Heat Shock Protein used to regulate steroid receptor binding to DNA?
HSP90
What is the receptor binding site sequence of the transcriptional coactivators?
LLxxLL
L: leucine
x: any AA
Do TRs need hormones to bind DNA?
Not necessarily
How is thyroid receptor activation of DNA transcription regulated?
Suppressor proteins that are released upon hormone binding due to a conformational change and coactivators bind
What molecules can bind hPPARs?
Arachidonic acid metabolites
What molecules bind hRARs?
All-trans retinoic acids
What molecules bind hRXRs?
9-cis retinoic acid
What is the main role of hRXRs? With which receptors?
Form heterodimers with other nuclear receptors
All except for steroid receptors: PPAR, RAR, TR, and VDR
What does the dissociation constant of a hormone correspond to?
The concentration of hormone that half saturates the receptor
What is equation to calculation the amount of hormone bound to a receptor?
Hormone bound = Max . [hormone] / Kd + [hormone]
Max = maximum possible hormone binding
When is regulation of the hormone binding to the receptor most powerful?
Around the Kd of that hormone
What is the purpose of a Stachard plot?
To find Kd
What are the 2 points to know on a Stachard plot?
- Slope = -1/Kd
2. x-intercept = # of binding sites (or receptors if only 1 binding site per receptor)
What does a steeper slope on a Stachard plot mean?
Tighter binding
What does a curve instead of a line on a Stachard plot mean?
Concentration is very far from the Kd OR receptors with different affinities to a hormone
Which receptor is used for comparison to all the others?
hGR
What allows the common structure of the hormone binding domain of nuclear receptors to bind different hormones?
The induced fit nature of it
Describe the specificity of the DNA binding domain of nuclear receptors.
Low DNA binding specificity (only 66 amino acids in this region). But the P box forms alpha helices that will enter the major grooves of DNA. Some of these alpha helices are important for specificity
How do most transcription factors interact with DNA?
By entering the major grooves
Which nuclear receptors can bind DNA as homodimers very EASILY?
Those that have palindromic DNA binding sequences: GR, MR, PR, AR, ER (all the steroid receptors), TR
What is the direct repeat DNA binding sequence used for in nuclear receptors?
Hetero OR homodimers
Why do different nuclear receptors have different spacing between their DNA binding sequences?
To make room for the different nuclear receptor
Why is it very easy to get mutations in the androgen receptor?
Because it’s X-linked
What is the Type 1 GR?
MR
What is the Type 2 GR?
GR
Type 2 diabetes drugs that increase the sensitivity to insulin target which type of nuclear receptors?
PPAR gamma
What are the 2 axis of a Statchard plot?
- x-axis: bound
2. y-axis: bound/free
What are the 2 axis of a hormone binding curve? What shift shows tighter binding?
- x-axis: log [hormone]
- y-axis: relative binding
LEFT SHIFT
What domain of the nuclear receptor determines what subclass the receptor belongs to?
DNA binding domain
What is the role of the 2 zinc fingers? Do they interact with the DNA?
To situate the P box in the right major groove of DNA
They do not interact with the DNA
