Nature's design of nanomotors.

The need for movement is an essential concept of all living organisms. On a macroscopic scale, animals and microbes have to be able to move towards food and away from poison and predators. Plants turn their leaves toward their energy source, the sunlight. But even on a molecular scale, movement is essential for life. It has been known for a long time that enzymes and proteins undergo large conformational changes while performing their biological tasks. The catalytically active regions of enzymes need to sequentially open to bind their respective substrates and close to allow the specific chemical reaction to occur in a defined chemical environment. The active sites finally open up again up to allow the product to be released. Molecular motors are proteins and protein complexes that have evolved in living cells to carry out a variety of functions essential for survival, reproduction and differentiation of the cells and organisms. They use chemical, electrochemical or potential energy and transduce that energy into physical, chemical or mechanical force. In this paper we review some of the molecular motors that were designed by nature to either perform physical work or that contain motor-like movements as part of their catalytic mechanism.