Protein Folding

[Alan J. Robinson]

I would like to thank all those who replied to my post about the 
signficance of the Ramachandran plot and whether it is consistent 
with the folding process.

I haven't had time to fully research this, but I'm now led to 
believe that Ramachandran's original figure was based on a simplified 
computer model of a polypeptide, with equal values for phi and for psi 
at each consecutive residue.  This more or less corresponds to the 
interior of secondary structure in native folded proteins.  Thus the 
Ramachandran plot is roughly what secondary structure is sterically 
possible in folded proteins, even before hydrogen bonding takes 
place.  

Real proteins are obviously more complex than this in several 
different ways, so that the values of phi and psi observed in practice 
don't always fall within the regions shown on the plot, and certainly 
don't constrain the folding process itself in any direct way (though 
obviosuly constrained by steric considerations too.)

Alan J. Robinson
robin073 at tc.umn.edu