Energetic costs, precision, and efficiency of a biological motor in cargo transport

Molecular motors play key roles in organizing the interior of cells. An efficient motor in cargo transport would travel with a high speed and a minimal error in transport time (or distance) while consuming minimal amount of energy. The travel distance and its variance of motor are, however, physically constrained by energy consumption, the principle of which has recently been formulated into the thermodynamic uncertainty relation. Here, we reinterpret the uncertainty measure ([Q]) defined in the thermodynamic uncertainty relation such that a motor efficient in cargo transport is characterized with a small [Q]. Analyses on the motility data from several types of molecular motors show that [Q] is a nonmonotic function of ATP concentration and load (f). For kinesin-1, [Q] is locally minimized at [ATP] {approx} 200 M and f {approx} 4 pN. Remarkably, for the mutant with a longer neck-linker this local minimum vanishes, and the energetic cost to achieve the same precision as the wild-type increases significantly, which underscores the importance of molecular structure in transport properties. For the biological motors studied here, their value of [Q] is semi-optimized under the cellular condition ([ATP] {approx} 1 mM, f = 0 - 1 pN). We find that among the motors, kinesin-1 at single molecule level is the most efficient in cargo transport.