  We analyze theoretically the effects of excluded-volume interactions between
motors on the dynamics of a cargo driven by multiple motors. The model
considered shares many commons with other recently proposed in the literature,
with the addition of direct interaction between motors and motor back steps.
The cargo is assumed to follow a continuum Langevin dynamics, while individual
motors evolve following a Monte Carlo algorithm based on experimentally
accessible probabilities for discrete forward and backward jumps, and
attachment and detachment rates. The links between cargo and motors are
considered as non linear springs. By means of numerical simulations we compute
the relevant quantities characterizing the dynamical properties of the system,
and we compare the results to those for non interacting motors. We find that
interactions lead to quite relevant changes in the force-velocity relation for
cargo, with a considerable reduction of the stall force, and cause also a
notable decrease of the run length. These effects are mainly due to
traffic-like phenomena in the microtubule. The consideration of several
parallel tracks for motors reduces such effects. However, we find that for
realistic values of the number of motors and the number of tracks, the
influence of interactions on the global parameters of transport of cargo are
far from being negligible. Our studies provide also an analysis of the
relevance of motor back steps on the modeling, and of the influence of
different assumptions for the detachment rates. In particular, we discuss these
two aspects in connection with the possibility of observing processive back
motion of cargo at large load forces.
