Signal Transduction Flashcards
Post-Translational Modification
Most important in multicellular eukaryotes
Phosphorylation
Acetylation
Methylation
Ubiquitnination
Effects: change surface properties of protein
Why Phosphate as PTM?
Phosphate is big and has highly [ ] negative charge
ATP readily acts as phosphate donor
Reactions are thermo favorable but kinetcally slow and thus can be enzymatically controlled
Which AA get phosphorylated
Serine and Threonine (both have free OH) done by same/similar enzyme
Tyrosine only found in multicellular animals
Assembly and Disassembly of Signaling Complexes
Alter subecellular localization of proteins
Associate enzymes with their substrate
Assemble complex multifunctional strucutres that can integrate and coordinate activites
Writer vs. Eraser
Writer puts something on protein, eraser removes it.
i.e. kinase = writer, phosphatase = eraser
Kd
Dissociation constant
At equilibrium kon [A][B] = koff [AB]
Kd = Koff / Kon = [A][B] / [AB]
Kd has units of concentration
What does Kd mean?
Kd is [ ] of B at which half of A is free and half is bound to B
If B > Kd then most of A is bound to B
If B < Kd then most of A is free
Fractional Occupancy
F.O = [B] / (Kd + [B])
Which has the greater affinity for substrate?
Kd1 = 10^-15 or Kd2 = 10^-4
Kd1 => less substrate is free and majority is bound to enzyme
NB: Kd = Koff / Kon = [A]*[B] / [AB]
Affinity
Measure of how likely two components are to bind to each other at a given [ ]
Specifity
Measure of the affinity of two components compared to the affinity of other possible binding partners
Regulated Subcellular Localization of Signaling Proteins
Substrates are not uniformly distributed in the cell. The activity of a protein will depend on the local [ ] of these partners
Regulated by transcription and membrane localization
JAK / STATS is an example of?
Nuclear Localization
Prolactin binds to receptor. Activated receptor activates JAK protein via phosphorylation. JAK protein causes STAT to dimerize becoming active.
Active STAT acts as transcription factor.
Regulation of protein conformation in signaling
Same protein can exist in multiple 3D conformations, which have different activities
i.e. Calmodulin, Hemoglobin
Catalytic Properties of Signaling Proteins
Potential for large signal amplification action at a distance
i.e. Caspase cascade
Small molecule Second messenger
Signal leads to production of highly diffusible product that can regulate downstream effectors
i.e. cAMP, Ca2+, IP3 and DAG
NB: Secondary messengers are small
Modular Architecture
Conserved domains of proteins are rearranged to create complex proteins
Domain
A compact, independently folding unit of protein structure.
i.e. Rho GEF
Modular Signaling Proteins Scaffold
These types of proteins allow for binding of specific substrate to the specific enzyme. Scaffolding protein increase specificity.
G Proteins
Have slow intrinsic GTPase activity
Normally only active in GTP state
Release of GDP (Koff) is very slow
GEF (Guanine Exchange Factor) promotes activiation
GAP (GTPase Activator Protein) promotes turning off G-Protein
G-Protein Coupled Receptors
Can act as GEFs
Getting Information Across the membrane
Use readily diffusable proteins
i.e. NO or Hormones
Bind to receptors to relay message
i.e. G proteins
Tyrosine Kinase Receptors
Gated Ion Channels
i.e. Ca++ ion channel with Vassopressin
