Lipophilic Steriod Hormones transverse PM to bind Intracellular Receptors

1
Lipophilic Steriod Hormones transverse PM to bind
Intracellular Receptors
Figure 20-2
2
Steriod Hormones Receptors

• Sex hormones, cortisol, ecdysone, Vitamin A and D
• Very stable (t1/2 is days/hours) to mediate long
  lasting responses
• All receptors bind DNA to act as TFs (often Zn
  finger family members), some enter nucleus only
  when bound to ligand, others (retinoic acid/ vit.
  A) bind DNA in absence of ligand-here change in
  conformation leads to activation/suppression of
  transcription.
• Hsp90 is inhibitory protein that complexes with
  cytoplasmic form of these receptors in absence of
  ligand to keep from entering the nucleus
  (chaperone). Binding of hormone ligand displaces
  chaperone to allow nuclear entry.

3
Other signals require cell surface receptors
Figure 20-2
4
Some Cell Surface Receptors Are Linked or
Otherwise Associated with Tyrosine Kinase Enzymes
Figure 20-3c
5
Some Cell Surface Receptors Have Their Own
Intrinsic Enzymatic Activity
Figure 20-3d
6
Some Cell Surface Receptors Act as Gated Ion
Channels
7
G-protein Coupled Receptors (GPCRs) Are an
Important Type of Cell Surface Receptor
Many sensory systems rely on such pathways
Figure 20-3a
8
GPCRs Act Through 2nd Messengers
Figure 20-4
9
Common Signaling Proteins G-proteins
Bind GDP/GTP Often Have Inherent GTPase Activity
Figure 20-5a
10
Common Signaling Proteins Protein Kinase Cascades
Figure 20-5b
11
Common Signaling Proteins Adaptor Proteins That
Form Novel Signaling Complexes!
Figure 20-5c
12
Overall, these are the basic themes that we will
examine in more detail
Figure 20-6
13
Identification and purification of cell-surface
receptors
Receptors are detected by binding assays with
I125 ligands
Note saturation effect
Uptake of label in the Presence of 100x excess
Of cold ligand (all specific Sites are
saturated)
Figure 20-7
14
KD values for cell-surface receptors approximate
the concentration of circulating hormones
Figure 20-8
Often 50 of maximal physiological response
occurs at a ligand concentration significantly
lower than KD
15
Molecular Biology Many receptors can be cloned
without prior purification
Receptors proteins also are purified by affinity
techniques
Figure 20-9
16
G protein-coupled receptors and their effectors

• Ligand binding activates the receptor, which
  activates the G protein, which activates an
  effector enzyme to generate an intracellular
  second messenger
• Many different mammalian cell-surface receptors
  are coupled to a trimeric signal-transducing G
  protein
• All G protein-coupled receptors (GPCRs) contain 7
  membrane-spanning regions with their N-terminus
  on the exoplasmic face and C-terminus on the
  cytosolic face
• GPCRs are involved in a range of signaling
  pathways, including light detection, odorant
  detection, and detection of certain hormones and
  neurotransmitters

17
GPCRs all share a common structure with 7 TM
domains
Figure 20-10
18
GPCRs can also display considerable diversity in
structure
V1Rsubfamily/G?I distantly related to T2Rfamily
V2R subfamily/G?o Similar to T1R1/R2,glutamateRs,
Ca-sensingR Long Divergent N-tail
19
Trimeric Gs protein links GPCRs and Adenylyl
Cyclase
Figure 20-16
20
GPCRs act through 2nd Messengers
cAMP and cGMP are both rapidly degraded By
respective PHOSPHODIESTERASE ENZYMES
Figure 20-4
21
Adenyl Cyclase (AC) Is a Highly Conserved
Effector Protein That Has Many Isoforms
Figure 20-15
22
The Basic cycle for GPCR coupled G-proteins is
sensitive to the effects of agents such as
Cholera toxin (the product of Vibro cholera and
the source of cholera) which causes persistent
activation of AC in intestinal epithelial cells
leading to massive H2O uptake and diarrhea
Figure 20-17
23
Activation and Inhibition of AC by Gsa and Gia
Figure 20-18
24
Different AC isoforms respond to alternate
G-protein subunits
Figure 20-43