13 - Protein Folding (unfinsihed)

When do proteins fold for function

Immediately after coming out of ribosome

What does molten globule allow for

Adjustments in side chains and secondary structure

When are some proteins completely functional

Upon release of C-terminal end from ribosome

How does protein folding happen

As the chain is coming out of the ribosome

What does folding do

Change 3d structure

What do molecular chaperones do

Meet proteins at the ribosomes

Which are the heat shock proteins

Hsp60 and hsp70

What do chaperone proteins do

Have specific functions in altering a misfolded protein

What does hsp70 do

Initiates early protein folding

What does hsp70 look for

Stretches of hydrophobic amino acids which trigger ATP hydrolysis

Procedure of hsp70

Clamps down on hydrophobic region and delays folding until entire hydrophobic stretch has emerged

What are the 3 stages of protein folding

Newly synthesized protein can:

1. Correctly folded without help

2. Correctly folded with help of a molecular chaperone

3. Incompletely folded and digested by the proteasome

What is there a competition of in regards to proteins

Competition between chaperones and proteasomes to fix a protein

How are size and degradation of a protein related

The longer a protein is misfolded, the more likely it will be degraded

What is the proteosome structure similar to

Hsp60 family chaperones

Structure of protasomes

Have a cylinder that contains proteases for digestion of protein

How. Does Hsp60 work

Incorrectly folded protein goes into hsp, GroES cap binds to top, correctly folded protein comes out

three structural parts of a proteasome

Two caps and one cylinder

What do the caps do in proteasome

Bind ubiquitin marked proteins to keep proteases in

Main purpose of proteasomes

Swallow nad protein and unfold it

How does the cylinder (middle part of proteasome) work

Has active sites for binding

What do the proteases do to proteins

Digest them into short peptides

What does it mean by proteasomes have high processivity

Once they get a protein, they don’t let go until it is converted to short peptides all the way

What is ubiquitin

A highly conserved eukaryotic protein

What is one of the functions of ubiquitin

Serve as a recognition marker for proteasomes when it is bound to misfolded proteins

What cellular processes does the ubiquitylation system function in

1. Antigen