A two-dimensional model for kinesin and dynein stepping along microtubules

Recent experimental observations of kinesin and dynein motion on microtubul es (Wang Z. et al, Biophys. J., 69 (1995) 2011) have shown that kinesin mov es (mainly) along one single protofilament, while dynein trajectories visit often several protofilaments. By modeling these proteins as dimers of elas tically coupled Brownian particles moving on a two-dimensional washboard po tential, under non-equilibrium conditions, we Show that both types of behav iour are qualitatively reproduced by simple changes of the characteristics of the elastic coupling. Our results suggest the possible relevance of the neck region flexibility in explaining the functional differences of these m olecular motors.