10 - Bio-inspired molecular motors

Summary

Nanotechnology, usually defined as the manipulation of matter on a scale with at least one typical dimension in the range from 1 to 100 nanometers, is still hailed as the most promising technological revolution of the twenty-first century. Biology clearly demonstrates that all sort of molecular machines with many different functions, fully capable of producing and even repairing damaged functional units, are possible at this scale. While artificial molecular machines are still no match for the exquisite biological machines existing in nature, and the expected technological revolution is still far away, there have been some breakthroughs, proof-of-principle experiments, built on or inspired by their biological counterparts.

Central to these machines are the molecular motors that convert some sort of energy, usually chemical or light, into mechanical work. Their operating mechanism is based on the ratchet principle, with thermal noise playing an unavoidable role at the nanoscale. In most motors, biological or artificial, there are chemical reactions in which the random motion provoked by thermal noise allows the system to surmount kinetic barriers, an essential step required for the operation of the machine.

The actions of individual molecular motors is connected with the macroscopic world by means of bottom-up approaches. One way to arrange smaller components into more complex assemblies is borrowed directly from biology, using base pairing to construct well-defined structures out of existing DNA. Other techniques use selfassembly methods to attach motors to solid state structures or surfaces.

This chapter reviews some of the recent advances in the engineering of artificial molecular motors.

Artificial protein motors

Proteins are naturally assembled from their basic building blocks, amino acid units, using the information encoded in the DNA. Current techniques allow the synthesis of proteins in the laboratory from a given DNA fragment or a similar nucleic acid. This has permitted the generation of new protein motors with additional abilities and functions.

As discussed in Chapter 3, linear protein motors usually walk along cytoskeletal filaments in one direction only. Within the family of myosins, most observed motors move toward the positive end of the track, actin filaments, which are electrically polarized. One exception is myosin-VI, which moves backward toward the negative end of the polarized filament.

In order to better understand the mechanism of directionality in myosins, Tsiavaliaris et al. (2004) engineered two types of molecular motors, one based on myosin-I and another on myosin-II, both well-known forward moving motors.