Re: CCL:Levinthal's paradox

In highly nonlinear systems sudden transitions in states (from one to
 another) are a well known behavior.  Could it be that the 'paradox' is just
 the result of a simple state change in a protein driven by the highly
 nonlinear forces that control its configuration?
 Jim
 Check out my web site  http://www.kressworks.com/
 It'll blow your mind (politically), stimulate your senses (artistically)
 and provide scientific insights that boggle the mind!
 ----- Original Message -----
 From: Peter Shenkin <shenkin %! at !% schrodinger.com>
 To: <chemistry %! at !% ccl.net>
 Sent: Friday, July 30, 1999 4:35 PM
 Subject: CCL:Levinthal's paradox
 > On Fri, 30 Jul 1999, JATI KASTANJA wrote:
 > > does anyone know something about the Levinthal paradox?
 > >...
 > > Until now I am unsuccessful in finding out the journal where Cyrus ...
 >
 > Hi,
 >
 > If you do find the Journal, you will find that it contains only
 > a passing reference to what has become known as the Levinthal
 > paradox.  The idea really derives from a comment Cyrus once made at a
 > meeting.
 >
 > The idea is this.  Take a 100-residue protein.  Let's suppose each
 > residue can have only, say, 3 conformational states.  Then there
 > are 3^100, or about 10^48, possible states.  Now suppose the protein
 > can explore a new state with every moleculear vibration.  Suppose
 > each vibration takes about a femtosecond.  Then exploring all
 > the states would take about 10^48 fs, or 10^33 s.  There are about 10^8 s
 > in a year, so exploring all the states would take about 10^25 years.
 > But this is longer than the age of the universe.
 >
 > Now, in order for a protein to fold into its global
 > thermodynamic energy minimum, the folding process has to
 > be ergodic.  That is, it has to explore all its states
 > within the time-span of the process.  But protein folding takes
 > typically seconds to minutes.  So a protein can't be folding
 > into its thermodynamic energetic minimum, since it can't
 > possibly find it in so short a time.
 >
 > Therefore, protein folding must be a kinetically controlled process.
 > I.e., proteins fold to the most accessible minimum, rather than the
 > most stable minimum.  In this, protein folding must resemble the
 > kinetically controlled reactions of organic (and bio-) chemistry.
 >
 > The reason it's considered a "paradox" is that most people
 > don't believe it (at least for globular proteins as small
 > as 100 residues). Cyrus didn't believe it either, in fact.
 > But it is fun to think about, and it's great for impressing
 > people at cocktail parties.  (You have to go to the right cocktail
 > parties, though. :-) )
 >
 > -P.
 >
 > --
 > ********* Peter S. Shenkin; Schrodinger, Inc.; (201)433-2014 x111
 *********
 > *********** shenkin %! at !% schrodinger.com; http://www.schrodinger.com
 ***********
 >
 >
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