Transcript Getting things where they need to go: Protein Targeting

Getting things where they need to go: Protein Targeting
Translation: Converting nucleotide sequence to
amino acid chain
Role of tRNA, base pairing and wobble
Role of ribosome (A, P, E sites)
CBI 6.4
CBI 6.5
Neurotransmitters: synthesis and packaging
Where are neurotransmitters/neuropeptides synthesized?
Cell
packaging
What must happen before they
can be used?
Barriers to packaging
Biological membrane of vesicle
Polar nature of neurotransmitter
How are the barriers overcome?
transport
Carrier Proteins
Why are they needed?
How do they work?
What kind of energy is needed?
Main Classes: Passive versus Active Transport
Going with or against the flow
Types of active transport:
Coupled– ex. symports or antiports
Pumps– like STE6, mdr, Ca++ pump (ATP hydrolysis)
Light driven pumps (primarily bacterial)
Which class(es) likely to be used in initial packaging of
neurotransmitters? In their re-uptake?
Neurotransmitter receptor: synthesis and packaging
Is a neurotransmitter receptor a cytosolic protein?
Cell
Where is it synthesized?
How does it get into a membrane?
?
?
Cytosolic vs. Noncytosolic proteins
The catecholamine theory of affective disorder
What sorts of situations could result in this condition?
(what would alter the amount of signaling at a synapse?)
1) Don’t make enough neurotransmitter
2) Make it but don’t package it into vesicles
or don’t release it correctly
3) Make/ release but receptor not present on post synaptic cell
or not functioning correctly
4) Make/ Release/ Receptor there but overactive re-uptake
reduces the ‘effective’ amount of neurotransmitter
Importance of specific translocation
>50% of protein made on cytosolic ribosomes are not intended
to be used in the cytosol
Must cross between 1 and 3 membranes to reach final destination
Mis-localization can have drastic consequences—disease or death
How does the cell know where to place a protein?
Cellular ‘ZIP code’
Signal Sequences and Signal Patches
Signal sequences
How are these signals used?
Necessary and sufficient
Targeting to the ER
If targeted to the ER where can a protein end up?
Main point of entry into the endomembrane system
TWO methods of targeting to ER
Minor pathway: Sec-dependent translocation
Identified first in bacterial genetic screens
Post translational
Post-translational translocation
Sec- dependent
Co-translational translocation
Major pathway: SRP-dependent translocation
First identified in in vitro experiments using canine microsomes
and wheat germ translation systems
Co-translational
CBI 12.3
Co-translational translocation
Important components from ER: SRP- receptor, TRAM
Sec61 complex (& BiP/Kar2-- sometimes)
Mammals: ER translocation involves “push”
Yeast: ER translocation involves “push” and “pull”
ER proteins
ER
Where can a protein end up in the ER? How does it get there?
Lumenal proteins
Single transmembrane span proteins
Multipass transmembrane proteins
What category do our neurotransmitter and
neurotransmitter receptor fall in?