the puzzle of chaperones!

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k3nz3n
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the puzzle of chaperones!

Post by k3nz3n » Tue May 02, 2006 5:09 pm

chaperones are molecules that help fold proteins that are synthesized right? from what i know, about ~80% of proteins use chaperones as a 'guide' to help them fold.. I do realise that most proteins also can fold themselves without the help of chaperones (Hsp 70) or chaperonins (Hsp 60)..

but the question is how do chaperones or chaperonins themselves manage to fold in the correct order?

i do realise that maybe the chaperones can without any help fold themselves to the right order, however, i do not think it is THAT simple? i havent got a single clue, if im still stumped, i think ill keep the answer as they fold naturally themselves.. if anybody got a better suggestion please please enlighten me :)

rg
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Post by rg » Fri May 05, 2006 6:35 pm

chaperons are old protiens that help guiding the newly synthesised protiens to aquire their quaternary structure.....just as grandparents guide the path of a child so are the chaperons like the grandparents and new protiens like children....it may be probably due to the bonding interactions between them...like hydrophobic ,ionic,hydrogen or disulphide bonding.....

Ultrashogun
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Post by Ultrashogun » Fri May 05, 2006 8:19 pm

chaperons are old protiens that help guiding the newly synthesised protiens to aquire their quaternary structure


Dont chaperones assist in the formation of the terziarie structure?

I would guess that chaperones, or at least the chaperones of the chaperones assemble themselves with complete auto assembly.

On the other hand, if you look at how the proteins assemble themselves you can think of their state moving on a field of local minima of G, being guided toward the absolute mininum of G, with some minima of G "outside the course", in other words traps, from which chaperones must free the protein, for example the formation of a cis peptidic group in 1 of 4 residues of proline.

Notice the "1 in 4", if a protein makes it to the absolute min of G or not becomes a statistic question and a fraction of them will always make it on their own, if these are the chaperones then the correctly formed chaperones could assist in the correct folding of the "trapped" chaperone proteins.

Im guessing that this would make a nice exponential growth curve if we put the concentration of correctly folded proteins in funtion of the reactiontime.

dae
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Post by dae » Sun May 07, 2006 3:11 am

First off, thanks for the nice metaphor, I laughed out loud.
rg wrote:just as grandparents guide the path of a child so are the chaperons like the grandparents and new protiens like children.

However, I'm not sure that it actualy has anything to do with the topic at hand.

I can't contribute much to the general question, in fact I suspect that the process is specialized and diverse for different classes of proteins. What I do know is that the chaperone proteins you mentioned, Hsp 70 & 60, are "heat shock proteins" that actually unfold proteins. From Wikipedia,
Although most newly synthesized proteins can fold in absence of chaperones, a minority strictly requires them.
So the main function of heat-shock proteins is to refold miss-folded proteins (the name suggests this, these proteins are expressed in especially high concentration during heat shock because the heat promotes the denaturing of correctly folded proteins), cf. prions. Heat shock proteins also assist in the import of nuclear proteins into mitochondria and chloroplast by denaturing them and passing them through a pore (TOM/Tim23 complex in mitochondria).
Although I have no source for this, I believe it is a logical conclusion that the proteins that strictly require chaperone proteins evolved after the chaperone proteins, opposed to the chaperone proteins taking the place of another scaffolding system.

I agree with Ultrashogun when he points out that proper folding is a mater of statistics. Chaperone proteins serve to shift that statistic in a positive fashion.

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Post by LilKim » Sun May 07, 2006 3:30 am

hey...

Yeah, I'm not so sure about the old-protein new protein metaphor. because I know that many chaperones are resident and transmemrane protiens that generally don't leave the endoplasmic reticulum. (yet i'm sure that there other others too .. that are not in the ER)

For a LONG time I believed that chaperones were proteins necessary for folding nacent proteins. However, i went to a recent lecture and the guest lecturer made it a POINT to explain to us that chaperones actually keep proteins UNFOLDED!!! Therefore, they can then fold at a later time in a domain specific sequence... ultimately creating the correct structural conformation in a sequential manner.

Anyways.. i haven't studied anything or read anything directly that agrees with the guest lecturer ... so i'm just going to assume that he's correct.

and heat shock proteins ... not sure what they do normally... so i can't shed any light on that one (Dae's comment makes sense though....)

kewl beans!
- KIM

dae
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Post by dae » Sun May 07, 2006 3:53 am

You're exactly right. Heat shock proteins are chaperone proteins, I was using them as an example as how the broader class of chaperones might work. Thanks for confirming my assumption.

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