  Recent experiments have demonstrated that dynein motor exhibits catch bonding
behaviour, in which the unbinding rate of a single dynein decreases with
increasing force, for a certain range of force. Motivated by these experiments,
we propose a model for catch bonding in dynein using a threshold force bond
deformation (TFBD) model wherein catch bonding sets in beyond a critical
applied load force. We study the effect of catch bonding on unidirectional
transport properties of cellular cargo carried by multiple dynein motors within
the framework of this model. We find catch bonding can result in dramatic
changes in the transport properties, which are in sharp contrast to kinesin
driven unidirectional transport, where catch bonding is absent. We predict
that, under certain conditions, the average velocity of the cellular cargo can
actually increase as applied load is increased. We characterize the transport
properties in terms of a velocity profile phase plot in the parameter space of
the catch bond strength and the stall force of the motor. This phase plot
yields predictions that may be experimentally accessed by suitable
modifications of motor transport and binding properties. Our work necessitates
a reexamination of existing theories of collective bidirectional transport of
cellular cargo where the catch bond effect of dynein described in this paper is
expected to play a crucial role.
