Nv. Buchete et Je. Straub, Mean first-passage time calculations for the coil-to-helix transition: Theactive helix Ising model, J PHYS CH B, 105(28), 2001, pp. 6684-6697
The kinetics and thermodynamics of the coil-to-helix transition is studied
using a one-dimensional "Zimm-Bragg" Ising model. The mean first-passage ti
me for the coil-to-helix transition is estimated within the "mean sequence"
approximation. A generalized mean first-passage time equation is derived w
here the transition rates may depend on the state of the system. The analyt
ic expression for the mean first-passage time is evaluated, and the results
are discussed as a function of energetic parameters. nucleation and propag
ation constants, peptide length, and the initial fraction of coil. The equi
librium thermodynamic properties of the model are shown to agree well with
the Zimm-Bragg model, validating the mean sequence approximation. The time
scales for helix formation are computed for a range of energetic parameters
that determine the nucleation and propagation constants for the model. It
is shown that, for a range of thermodynamically realistic parameters, the k
inetic first-passage times are on the order of those measured experimentall
y. The mean first-passage time approach implicitly allows for the possibili
ty of multiple helix nucleation sites and multiple helical domains and make
s no assumptions regarding the unidirectionality of helix propagation. Comp
arison is made with the predictions of the "sequential kinetics" model of B
rooks and the "kinetic zipper" model of Thompson et al. Extension of the mo
del to the more general case of structure formation in proteins is discusse
d.