Curious finding
In fruit fly larval
When the temperature goes up from normal 25ºC to 32ºC
activate
A number of new sites on the giant chromosome
conclusion
In every type of organism, from bacteria to plants and mammals
Temperature goes up induce The expression of new genes
This response is called the heat shock response and the protein which was produced during heat shock is called Heat Shock Protein(Hsp).
PS: Hsps were found not only in heat shocked cells, but also at lower concentration in cells under normal condition
What is the function of these so-called Hsps?
•binding protein (Bip) ------- promote protein assemble
•Molecular chaperones •Hsp60
Binding protein (Bip) ------- promote protein assemble
The discovery of Bip:
A.In bacteriophage, a protein encoded by the bacterial chromosome participates in the assembly of virus particles, even though this host protein was not a component of the final virus particles. (e.g.: GroE talk about it latter )
Binding protein (Bip) ------- promote protein assemble
B. In plant, a similar assembly-promoting protein in chloroplast was found in pea plant
Rubisco is composed of 16 subunits: 8 large subunits and 8 small subunits. And the assembly-prom
oting proteins are bind to large subunit
C. In mammal, there are also some proteins which binds to the heavy chain that will assist the assembly of multisubunit proteins but is not found in final complex.
Binding protein (Bip) ------- promote protein assembly
D. Binding protein(Bip): the protein associate with newly synthesized heavy chain.and
it can promote protein assembly.
Molecular chaperone
Temperature sensitive protein:
1. Sensitive to temperature2. Small rise in temperature causing this delicate molecule to unfold3. Under heat shock, soluble protein became denatured and aggregated
Molecular chaperone:
Temperature goes up Molecular chaperone synthesize
Bind to aggregated protein
Promote disaggregation
Function: assist the assembly of proteins by preventing undesirable interaction and assist polypeptide chain folding.
Classification of molecular chaperone:
Example
Molecular chaperone
Hsp 90
Hsp 70: Bip
Hsp 60: GroE
sHsp
Hsp 60 ------ best understood chaperone
Use GroE as an example: GroE is composed of 2 separate proteins GroEl and Gro ES
A model of GroEL:• Data from electron microscope• 14 polypeptide subunits arranged in 2 stacked rings resembling a double doughnut
Reconstruction of GroEl based on High-resolution electron microscope
A BGroEL GroES bind toGroEl
Centralcavity
Hsp 60 ------ best understood chaperone
The binding of GroES to GroEL will lead to comformation
changes
The binding of GroES cap is accompanied by a 60º rotation of
apical domain 60º
Hsp 60 ------ best understood chaperone
Nonnative polypeptide enter and bind to the hydrophobic site of GroEl
Binding of GroES cap produce conformational changes and release of pol
ypeptide.
The GroES dissociate Native polypeptide is ejected.Misfold ones rebind to GroEl
chamber.
Hsp 60 ------ best understood chaperone
How it is possible for a chaperone to bind so many different polypeptide?
The binding site has structural flexibility that allows it to adjust its shape to fit the shape of the particular
polypeptide with which it has to interact.
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