BIOMOTORS

A Comprehensive Review On Its Use in Nano-biotechnology

Concept of a ‘Motor’

• A motor is essentially a machine, that is capable of producing motion or enabling a change in energy from one state to another.

• Advances in technology have boosted the need for nano-scale motors.

• However, one of the main hindrances that have been encountered is the inability to just down-size or miniaturize the blueprints of a machine.

• However, one can take inspiration from Mother Nature, where we find several naturally existing nanomotors.

What are biomotors?

• Biomotors are basically molecular motors, whose components consist of molecules or atoms.

• These are already existent in nature and we find several such biomotors in the tiny cells of all organisms from bacteria (motors for the movement of the flagella) to humans (the cilia of the lungs).

• These biomotors have great significance in Biomolecular Nanotechnology, in which they use the knowledge of naturally occurring molecular motors to construct synthetic biomotors.

Biomotors (contd.)…• Biomotors can be defined as protein molecules that

convert chemical energy into mechanical motion. • Several types of synthetic biomotors are being

constructed based on the design and working of cellular motor proteins such as myosin, which is responsible for muscular contraction.

• Bacterial cells are actually proving to be the ideal ‘power generators’ for these micro-scale biomotors. Their motility in liquid media may be exploited to either push or pull micro-fabricated features in the form of propellers or turbines.

Advantages of Biomotors• Biomotors are one of Nature’s various masterpieces. • Each motor unit has a size of ~ 10 nm, which is a thousand

times smaller than any man-made motors. This is of immense significance in the up-coming technology-related fields such an nanotechnology and biotechnology.

• Also, the fuel efficiency of biomotors is higher than any existing man-made engines.

• One of the most important aspects of biomotors is the fact that it is eco-friendly and thus it reduces the carbon footprint. With the growing concerns over global warming, this has been welcomes with open arms.

Motor Proteins in Nanotechnology• A living cell can be viewed as a miniature factory, that contains a large

number of dedicated protein machines. • A cell has the remarkable ability to create a full copy of itself in less than an

hour, ; it can proofread and repair errors in its own DNA, sense its environment and respond to it, change its shape and morphology, and obtain energy from photosynthesis or metabolism, using principles that are similar to solar cells or batteries.

• All this functionality derives from thousands of sophisticated proteins, optimized by billions of years of evolution.

• Motor proteins represent a unique class of enzymes and enzyme complexes that convert chemical energy into mechanical work with relatively high efficiency.

• In these proteins, energy associated with catalysis (or an electrochemical gradient) is linked to conformational changes in the structure.

Types of Motor ProteinsRotary

Motors

• Rotary motors comprise of shafts and bearings.

• The bacterial flagellar motor is a classic example of a rotary motor.

• The complex uses a proton gradient to propel a large flagellum at speeds of up to 300 rps, and produces a rotary torque in excess of 550 pN nm.

• A second rotary motor, ATP synthase (F0F1-ATPase), is a ubiquitous enzyme complex responsible for proton-powered production of adenosine 5 -′triphosphate (ATP) in living systems.

Linear Motors

• Linear motors that move along tracks in a step-by-step fashion.

• There are a large number of natural designs of linear motors for functions ranging from muscle contraction to vesicle transport .

• Linear motors can be chosen from three principal families: • myosins—moving along actin

filaments toward the barbed end;• kinesins—moving along

microtubules toward the plus end;• dyneins—moving along microtubules

toward the minus end.

Motor Proteins in a Synthetic Environment : Hybrid devices

• Due to dramatic progress of nanotechnology and biological science, biological molecules (e.g. DNA and proteins) can now be combined with solid nanostructures (e.g. nanoparticles and nanowires) to build a new generation of devices.

• These include biological sensors and nanomechanical systems based on protein motors. These new types of devices are called hybrid devices.

Hybrid devices: Contd..

Regulating Biomolecular Motor Activity

Strategies employed to regulate biomotor activity

Controlled release of the caged ATP into the solution to modulate the linear translation of conventional

kinesin.

Genetic engineering of allosteric effector site into the catalytic domain

of the F1-ATPase molecular motor.

• A fundamental element in the engineering of biomolecular motor-powered devices and materials is the ability to modulate the activity of the motors. To date, two strategies have been used to regulate the functionality of biomolecular motors in synthetic systems.

Examples of Biomotors1) Nickel Nanopropeller: This biomotor rotates through the action of an engineered F1-ATPase motor . The directed assembly of the devices was controlled through genetic engineering of histidine tags that stuck the F1-ATPase onto nickel posts, with its central stalk protruding upwards. This connected to a nickel propeller of ~1 mm length through biotin-streptavidin bonds. Addition of ATP caused rotation of the propeller. A metal-binding site was engineered into the motor and acted as a reversible on-off switch by obstructing the rotation upon binding of a zinc ion , similar to the action of putting a stick between two cogwheels.

NICKEL PROPELLORThe direct evidence for the chemical synthesis of ATP driven by mechanical energy by attaching a magnetic bead to the g-subunit of F1-ATPase and rotating it. Rotation in the appropriate direction resulted in ATP production. The rotary activity of F1-ATPase has been harnessed to develop motor prototypes by several groups.

This device provided over two hours of continuous rotation with a mean torque of ~ 20 pN nm at 50% efficiency.

2) Gliding bacteria : On a larger scale, the gliding bacteria have been used to power a micromechanical device comprising a cogwheel-shaped rotor of 20-mm diameter rotating in a silicon track. Bacteria adhered to the rotor, turning it with ~2 rpm . Typically a bacterium moves by a series of straight runs interrupted by random turns. But when a straight run happens to swim up a chemical gradient (for example, the scent of food becoming more intense closer to the food itself), the bacterium extends the length of the straight run. Because favorable runs last longer than those in unfavorable directions, the net effect is that the bacterium eventually converges on itstarget, even though it has no direct way to steer itself—a strategy called chemotaxis.Our nanomotors move faster at higher concentrations of fuel, and this tendency effectively lengthens their straight runs.Chemotaxis could lead to the design of “smart,” autonomous nanorobots, which could move independently toward their target.

Examples of biomotors

Examples of Biomotors Kinesin- and Myosin-Driven Transport on Chips :One vision is that motor proteins will be used for controlled cargo manipulation on a chip,with applications in sorting, separation, purification, or assembly of materials . To reachthis goal, one needs to develop controlled motion along specific routes and directions.

When filaments are absorbed randomly onto a substrate, the direction of cargo transport is random as well.Therefore, considerable effort has been directed at creating confined motility by employingeither chemical patterning of active motor proteins or fabricated topographical A combination of topographical and chemical patterning has proven to combine the best of both approaches.

Other Applications and Unrealised Potential

Progress in the field will likely come from integration of achievements of the past few years into more complete and functional devices Promising in this respect is the sol-gel packaging of vesicles containing bacteriorhodopsin, a lightdriven proton pump, and FOF1-ATP synthase. Upon illumination of these sol gels, protons are pumped into the vesicles and ATP is created outside the vesicle by the ATP synthase. Besides the excellent stability of these gels (bacteriorhodopsin continued functioning for a month), this technology provides a convenient packaging method and a way to use light energy for fueling devices. Another interesting development is the engineering of polypeptides that can specifically bind to inorganic materials .When engineered into motor proteins, this technology could provide new opportunities for motor-driven nanoscale assembly of different materials.A related but even more futuristic field is the development of artificial molecular machines . Artificial molecular machines are synthesized molecules that can switch between different shapes upon illumination with light or through electrochemical reactions.

ConclusionMotor proteins are fast and versatile nanomotors with high energy efficiency.

Inspired by the biological applications of motor proteins in intracellular transport and as actuators, a number of devices have been designed. Nature has mastered not only the design of nanoscale functional units but also the integration of these units into the sophisticated multipurpose subcellular or cellular systems. This research attempts to learn nature’s lessons and translate them into valuable engineering.

The small size and force-exerting capabilities of motor proteins and the range of opportunities for specific engineering give them unique advantages over current human-made motors.The exploration of biomotors in technology will thus remain an interdisciplinary playground for many years to come.