QUESTIONS: alpha-helix "signals" in proteins

Kenneth Prehoda kenp at banyo
Thu Jul 7 17:21:24 EST 1994

Mr Neville Steven Percy (spbcnsp at ucl.ac.uk) wrote:
: Loadsa people write:

: [...] Loadsa stuff -- an excellent thread! -- [...]

[stuff deleted]

: >Does a protein first fold into its secondary structure elements and then into its tertiary structure, afterwhich the original secondary structure elements
: >remain as before the folding into the tertiary structure?  (If yes or no, could
: >you please provide references).

: Yes, this is correct, but it should further be pointed out that in the lumen of
: the rough endoplasmic reticulum where all this folding of the nascent protein
: chain is going on, there are a great quantity of chaperone molecules.
: Chaperones serve to protect regions of secondary structure from the 
: potentially damaging effect of exposure to the aqueous environment, until the 
: entire protein has been synthesized and all the secondary structure elements 
: can align to one another and form the final tertiary configuration, at which 
: point the chaperone dis-associates, and leaves this to happen.

: I imagine the kinetics of interaction with chaperones is therefore very 
: important in vivo, if not in such in vitro systems as may be used for protein
: structure studies... but this is very IMHO, as there are obviously a lot more
: specialized people than myself contributing to this thread!   :)

It is far from certain that secondary structure forms before the global
fold is formed (framework model).  The hydrophobic collapse model
where nonpolar surface is buried before secondary structure forms
is just as likely at this point.

Also, as far as I know chaperones are simply catalysts and do not
affect the end state of protein folding.  The final native state
will be the same whether or not a chaperone is present - albeit
it much more slowly without.

: (Mad Cow Disease)       Neville Percy ;  spbcnsp at ucl.ac.uk          _.=~-.--=~
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:  BioMOO, the virtual reality for biologists; telnet bioinfo.weizmann.ac.il 8888
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-Ken Prehoda
kenp at nmrfam.wisc.edu

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