Journal of Chemical Physics, Vol.105, No.3, 1242-1269, 1996
Discrete Step Model of Helix-Coil Kinetics - Distribution of Fluctuation Times
A method is outlined for the computer simulation of the cooperative kinetics required to construct the distribution function for time intervals between fluctuations in conformational states in macromolecules. Using the helix-coil transition in polyamino acids as an example, we develop a Monte Carlo cellular automata approximation of the kinetics of this system in discrete time. This approximation is tested against a number of exact solutions for homopolymers and is then used to calculate moments of the distribution function for the time intervals between switches in conformational state at a given site (e.g., given a switch from coil to helix at zero time, how long will it take before the state switches back), The maximum-entropy method is used to construct the very broad distribution function from the moments. In heteropolymers the diffusion of helix-coil boundaries is reduced, helix being more localized on strong helix-forming residues. We investigate the effect of a specific sequence of amino acid residues on conformational fluctuations by using the known sigma and s values for the naturally occurring amino acids to simulate the kinetics of helix formation (limiting the range of cooperativity to the alpha-helix) in sperm whale myoglobin, giving the time evolution to the equilibrium probability profile in this system.