  Dynein motors exhibit catch bonding, where the unbinding rate of the motors
from microtubule filaments decreases with increasing opposing load. The
implications of this catch bond on the transport properties of dynein-driven
cargo are yet to be fully understood. In this context, optical trapping assays
constitute an important means of accurately measuring the forces generated by
molecular motor proteins. We investigate, using theory and stochastic
simulations, the transport properties of cargo transported by catch bonded
dynein molecular motors - both singly and in teams - in a harmonic potential,
which mimics the variable force experienced by cargo in an optical trap. We
estimate the biologically relevant measures of first passage time - the time
during which the cargo remains bound to the microtubule and detachment force
-the force at which the cargo unbinds from the microtubule, using both
two-dimensional and one-dimensional force balance frameworks. Our results
suggest that even for cargo transported by a single motor, catch bonding may
play a role depending on the force scale which marks the onset of the catch
bond. By comparing with experimental measurements on single dynein-driven
transport, we estimate realistic bounds of this catch bond force scale.
Generically, catch bonding results in increased persistent motion, and can also
generate non-monotonic behaviour of first passage times. For cargo transported
by multiple motors, emergent collective effects due to catch bonding can result
in non-trivial re-entrant phenomena wherein average first passage times and
detachment forces exhibit non-monotonic behaviour as a function of the stall
force and the motor velocity.
