Biosignaling

1
Biosignaling

• Signals outside cell have to have actions
  insidewithout getting in.

2
Signals (Physiological)

• Autocrine
• Paracrine
• Endocrine- usually referred to as hormone
• Hormone- substance synthesized in small amounts
  by an endocrine tissue and carried by blood to
  the target tissue
• Physiological concentration range 1091015 M

3
Classification of Hormones

• Location of receptor
• Group I (Lipophilic Hormones) Have Intracellular
  Receptors vs. group II (Hydrophilic Hormones)
  Have Cell Membrane Receptors
• 2. Nature of signal or second messenger
• 3. (Where produced)

4
Receptors Are All Proteins Which Have Two
Functional DomainsFig. 12-1(a) Lehninger POB 4th
Ed.

• 1. Recognition domain
• 2. Signaling domain

5
Receptors Amplify SignalsFig. 12-1(b) Lehninger
POB 4th Ed. Fig. 12-16 Lehninger POB 4th Ed.

• Signal Transduction Cascade

• Epinephrine example

6
Receptors Can Be Downregulated

• The reason drugs are not as effective when
  chronically abused
• Not the whole story concentration change seen
  by the receptor

7
ReceptorEnzymeFig. 12-10 Lehninger POB 4th Ed.

• Extracellular receptor, transmembrane domain,
  intracellular enzyme

8
ReceptorEnzyme

• Insulin as a well-understood example

9
Insulin Receptor is Activated in Presence of
Insulin by DimerizingFig. 12-29 (part) Lehninger
POB 4th Ed.

• Phosphorylation of receptor occurs
• It is an autophosphorylation
• It is an auto-crossphosphorylation

10
Tyrosine Kinase of Insulin Receptor Initiates the
Cascade

• IRS-1
• SH2 domain of Grb2 (Sarc homology)
• Sos
• Ras
• Raf-1
• MEK
• MAPK

11
Kinases, Kinases and More Kinases

• Tyr kinase
• Ser/Thr kinase
• PI kinase
• Protein kinase A, B, C?
• MAPK (mitogen activated protein kinase), MAPKK,
  MAPKKK, MAPKKKK, more?

12
Phosphatases Turn the Signal Back Off

• Protein tyrosine phosphatase Types 1, 2A and 2B
• More than 40 known

13
Serpentine Receptors are G-ProteinCoupled
14
Serpentine Receptors

• Snake their way across the membrane 7 times
• Recently (Nov. 2000) a 6-tm protein published
• ß-adrenergic receptor (for adrenaline) prototype

15
G-Proteins

• G-Protein- GTP binding protein
• Classically heterotrimeric aß?
• Gs stimulates adenylate cyclase
• Gi inhibits adenylate cyclase
• Golf functions in smelling (olfaction)
• Others exist

16
G-Proteins

• G-Protein- GTP binding protein
• Classically heterotrimeric aß?
• Gs stimulates adenylate cyclase
• Gi inhibits adenylate cyclase
• Golf functions in smelling (olfaction)
• Others exist

17
G-Protein FunctioningFig. 12-14 Lehninger POB
4th Ed.

• GDP bound by a in the heterotrimeric complex
• When ligand bound by serpentine receptor, GDP
  exchanged for GTP
• ß? dissociate as complex
• a-GTP effects adenylate cyclase

18
cAMP production
19
Second Messengers
20
cAMP Activates Protein Kinase AFig. 12-15 (a)
Lehninger POB 4th Ed.

• Tetramer regulatory subunit blocks active site
  of catalytic subunit
• Binding of cAMP causes dissociation and
  activation of PKA
• Kinase cascade on consensus sequence RRXS and
  KRXXS

21
A Large Amplification of Signal OccursFig. 12-16
Lehninger POB 4th Ed.
22
Many Proteins Regulated in This Way Consensus
SequencesTable 12-3 Lehninger POB 4th Ed.
23
Degradation of cAMP

• Phosphodiesterase cuts the 35 linkage
• Phosphodiesterase is very active (regulated by
  hormones), therefore cAMP has short half-life
• Methyl xanthines are phosphodiesterase inhibitors

24
Receptor Downregulation Leads to
DesensitizationFig. 12-17 Lehninger POB 4th Ed.
25
2nd Messenger is cGMP

• (One) ANF Atrial Natriuretic Factor
• High sodium in urine
• Diuresis (urine output)
• Vasodilation
• Inhibit aldosterone secretion (aldosterone makes
  you thirsty)
• So sequence is increased cGMP leads to
  increased protein kinase leads to phosphorylation
  of smooth muscle proteins ? leads to relaxation
  of smooth muscle and vasodilation

26
Ca2 as a Second Messenger
27
Much Experimental Evidence Points to Ca2 Acting
as a MessengerFig. 12-20 (a) Lehninger POB 4th
Ed.

• Hormone effects are blunted if cells are tested
  in a Ca2-free medium
• Hormone effects are mimicked by A23187 (a calcium
  ionophore)
• Addition of calcium affects some enzyme rates
• Hormones added to cells cause a change in Quin2
  or Fura2 fluorescence

28
Calcium MetabolismFig. 12-20 (b) Lehninger POB
4th Ed.

• Absorbed by small intestine under the influence
  of vitamin D
• Extracellular 5 mM
• Intracellular 0.1-10 µM
• Intra-mitochondrial or intra-ER 1-20 µM

29
Changing Cytoplasmic Calcium

• Hormones enhance membrane permeability Na/Ca2
  exchange high capacity low affinity
• Ca2/2H ATPase
• calcium in protons out low capacity high
  affinity for fine tuning of level
• Exchanges between cytoplasm and intracellular
  stores
• Calcitonin and PTH

30
DAG as a Second Messenger
31
DAG is Produced via PLC
32
PIP2 Formation
33
Protein Kinase C is Activated

• directly by DAG
• indirectly by IP3, via Ca2 release
• Phosphorylation cascade ensues

34
Other Interesting Things
35
ChannelsFig. 12-3 Lehninger POB 4th Ed.

• Previously NaK-ATPase

36
ChannelsFig. 12-2 (part) Lehninger POB 4th Ed.

• Previously NaK-ATPase
• gated ion channel

37
Theories Behind Gates They Are All CorrectFrom
?

• Ball and Chain
• Twist
• Pivot

38
Theories Behind Gates They Are All CorrectFig.
11-51 (b) Lehninger POB 4th Ed.

• Ball and Chain
• Twist
• Pivot

39
Theories Behind Gates They Are All CorrectFig.
11-37 Lehninger POB 4th Ed.

• Ball and Chain
• Twist
• Pivot

40
ChannelsFig. 13-2 (part) Lehninger POB 3rd Ed.

• Action Potential
• Small depolarization (from 60 to 40 mV) opens
  voltage-gated ion channels Na flows in
• Potential rises to 30 mV, Na channels close, K
  channels open, K streams out, lowering potential

• Previously NaK-ATPase
• gated ion channel
• voltage gated ion channel

41
Steroid Hormone Signaling
42
Group II Hormones

• Include steroids, iodothyronines, calcitriol and
  retinoids
• Lipophilic
• Transport proteins
• Long half-life
• Intracellular receptor
• Receptor-hormone complex is the signal (i.e. no
  second messenger system)

43
A Little Steroid Nomenclature

• -ol, -one
• ß is cis to 19-methyl

44
Steroid Hormone Receptor StructureFig. 28-31
Lehninger POB 4th Ed.
45
Hormone Response Element (HRE)
46
Hormone Classes

• Glucocorticoids, mineralcorticoids, Androgens

47
Pituitary and Hypothalmic Hormones

• Hypothalmic hormones released pulsatile (Hormones
  are diluted and cleared)
• Feedback loops exist
• GH, PRL (and CS) glycoprotein hormone group
  POMC family

48
One Example of Alternate CleavagesFig. 45-5
Harpers ROB 24th Ed.

• Different cell types within pituitary produce one
  hormone
• Occurs by making the same protein but cleaving it
  into different hormones