  Within living cells, the transport of cargo is accomplished by groups of
molecular motors. Such collective transport could utilize mechanisms which
emerge from inter-motor interactions in ways that are yet to be fully
understood. Here we combined experimental measurements of two-kinesin transport
with a theoretical framework to investigate the functional ramifications of
inter-motor interactions on individual motor function and collective cargo
transport. In contrast to kinesin's low sidestepping frequency when present as
a single motor, with exactly two kinesins per cargo, we observed substantial
motion perpendicular to the microtubule. Our model captures a
surface-associated mode of kinesin, which is only accessible via inter-motor
interference in groups, in which kinesin diffuses along the microtubule surface
and rapidly "hops" between protofilaments without dissociating from the
microtubule. Critically, each kinesin transitions dynamically between the
active stepping mode and this weak surface-associated mode enhancing local
exploration of the microtubule surface, possibly enabling cellular cargos to
overcome macromolecular crowding and to navigate obstacles along microtubule
tracks without sacrificing overall travel distance.
