PT - JOURNAL ARTICLE AU - David R. Slochower AU - Michael K. Gilson TI - The ubiquity of directional and reciprocating motion in enzymes out of equilibrium AID - 10.1101/121848 DP - 2017 Jan 01 TA - bioRxiv PG - 121848 4099 - http://biorxiv.org/content/early/2017/04/19/121848.short 4100 - http://biorxiv.org/content/early/2017/04/19/121848.full AB - A biological molecular motor is an enzyme that uses the free energy of an out-of-equilibrium chemical reaction to drive mechanical motion. This motion must have a specific direction to fulfill the motor’s functional role. For example, a corkscrew-shaped flagellum must rotate in the appropriate sense to propel the organism. The generation of directional motion appears to be a complex protein property, and it is not clear how the evolutionary leap from non-motor enzymes to molecular motors could have occurred. Indeed, the existence of biological molecular motors has been held up in the popular press as a mark against the theory of evolution1. Here, we provide evidence, based on atomistic simulations and kinetic modeling, that conformational switching of non-motor enzymes, induced by out-of-equilibrium substrate binding and catalysis, induces motor-like, directional torsional motions, as well as oar-like, reciprocating motions. Generalizing from these specific results, we provide an argument that virtually any chiral molecule undergoing conformational transitions out of equilibrium should be expected to undergo directional rotations on small and potentially large scales. Thus, the emergence of directional motion did not require an evolutionary leap. Instead, directional motion was present in the earliest enzymes, and only evolutionary optimization was needed for highly adapted motor proteins to emerge. Moreover, because chirality is a sine qua non for directional motion, the adaptive value of directional motors means that chirality itself is adaptive, so the need for directional motion may be one reason for the prevalence of chiral molecules in living systems. Finally, the ubiquity of driven molecular motions in enzymes catalyzing reactions out of equilibrium might help explain why the diffusion constants of some enzymes increase with their catalytic rate 2-4.