Jarosaw Pillardy,
Cezary Czaplewski,
Adam Liwo,
William J. Wedemeyer,
Jooyoung Lee,
Daniel R. Ripoll,
Piotr Arukowicz,
Stanisaw Odziej,
Yelena A. Arnautova, and
Harold A. Scheraga*
Baker Laboratory of Chemistry and Chemical Biology, Cornell University,
Ithaca, New York 14853-1301, Faculty of Chemistry, University of Gdask,
Sobieskiego 18, 80-952 Gdask, Poland, and Cornell Theory
Center, Ithaca, New York 14853-3801
Abstract:
The development of three physics-based energy functions (force fields),
designed to simulate the restricted free energy of proteins of the ,
, and /
structural classes, is described. Each force field corresponds to a particular
weighting of the united-residue (UNRES) interactions defined in earlier work.1-6
To find the optimal weights for the , ,
and /
force fields, both the Z-score and energy gap of the native versus
nonnative structures are minimized simultaneously for four benchmark proteins:
1pou (for the force field), 1tpm (for the
force field), and 1bdd and betanova (for the /
force field). The simultaneous minimization was carried out by using a novel
Monte Carlo method, Vector Monte Carlo (VMC). For -helical
proteins, another weighting of the UNRES interactions (denoted as the 0
force field) was developed; this fourth force field is described in a companion
publication (Lee, J. et al. J. Phys. Chem. B 2001, 105,
7291). The structural implications of the final weights of the four force
fields, i.e., the relative contributions of the various UNRES interactions to
stabilizing common structural motifs of proteins, are analyzed. The 0,
, ,
and /
force fields were used in the CASP4 exercise for ab initio protein-structure
prediction with reasonable success. Finally, using a simple model system it was
shown that the VMC protocol does not require exhaustive sampling of medium- and
high-energy structures in order to optimize the parameters of the potential
energy adequately.