DK
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 Posted: Thu Jul 10, 2008 7:50 pm Post subject: Re: Chaperones and Protein Folding |
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In article <g532nu$213d$1@darwin.ediacara.org>, "Doug Wedel" <dougwedel@earthlink.net> wrote:
[quote]Just read an interesting article on chaperones in the current Sci.Am. Their
central function remains that of promoting and enabling the proper 3-D
configuration of amino acid chains into finished protein, but many
additional functions involving intricate disassembly and reassembly of
proteins have also been found.
Question: does the current understanding of the elaborate involvement of
chaperones in protein folding mean that the old concept of "self assembly"
of proteins (in which the linear string of amino acids settles into
thermodynamic equilibrium) applies only to very short strings of amino
acids, and not to the longer ones which require the assistance of chaperones
which apparently mediate structures that do not always represent the
thermodynamically most efficient folding?
[/quote]
Protein folding is mostly kinetically trapped. Thermodynamics says
nothing about how fast things happen. That is, if you want to wait an
eternity for some poorly folding polypeptide to fold, you will eventually
find it folded. In that respect, it>s the chaperone act as enzymes that
catalyze protein folding. (Recall that enzymes don>t change
equilibrium, just just increase the rate with which it is achieved).
That said, some argue for the existence of proteins that are,
in their "native" conformation, represent essentially a folding
intermediate or a product of a side reaction. (That is, there are
conformers with lower free energy than the functional native
protein). Some argue against this possibility. Theoretically,
chaperones can force folding protein into a particular folding
intermediate in which the protein is kinetically trapped.
IMHO, the question is almost impossible to resolve
unambiguously.
DK |
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