The study of proteins has become one of the hottest topics in science in the last 20 years, and not just for biologists. Understanding the function of proteins, their structure, how they operate together in networks and so on has attracted scientists in disciplines as diverse as physics, mathematics and computer science. And now electronics engineers are joining the fray.
Today, Eleonora Alfinito at the University of Salento in Lecce, Italy and a few pals, outline how understanding and exploiting the electronic properties of proteins is leading to an entirely new discipline which they christen ‘proteotronics’.
Their story begins in 2007, when a team of French researchers carried out an experiment with a protein known as OR-17, a receptor protein in rats involved in smell and known to bond with fruity-smelling aldehydes such as octanal.
In the experiment, the researchers attached OR-17 to a gold electrode and then measured how the electrical impedance through the electrode changed with an increase in the concentration of octanal in the environment.
The impedance of OR-17 follows a specific pattern which makes the receptor act like a switch. In other words, when the receptor is not attached to octanal, the way current passes through it as voltage changes follows a specific curve. But when the receptor bonds with octanal, this so-called I-V curve undergoes a step-like change.
That’s an interesting property. It immediately suggests a way to use OR-17 to detect octanal. Simply measure the current and voltage through the receptors and look out for the step-like change that signals the presence of the aldehyde. Voila—an electronic nose.
Indeed, that’s what the French team proposed in 2007. But it left open a problem. Why do the electrical properties of OR-17 behave in this step-like way? That’s not easy to answer because proteins are hugely complex structures. And without a theoretical model of how a component works, it’s hard to use it in a practical device.
Now Alfinito and co have cracked this problem. These guys have created a model of the electronic properties of OR-17 based on the network of connections between the amino acids in the protein that make up its structure.
Since the amino acids form a web-like structure, it’s easy to imagine that the impedance is highly sensitive to the exact structure of the web. In that case, it would be hugely difficult to calculate. But Alfinito and co say not.
Instead, they have created a mathematical model that calculates the impedance based on a relatively simple model of this web. Since the electronic interaction between different amino acids is well known, they calculate the electronic properties based on this entire 3D structure.
But what Alfinito and co have done is find a way to do this that doesn’t become mired in labyrinthine complexity. Their technique, known as impedance network protein analogue, describes the electronic interactions across the protein using a set of equations that can be solved computationally. This is relatively quick because it is entirely linear. But the beauty of the technique is that nonlinearity can be introduced separately as needed.
And the results are impressive. Not only does this model describe the electronic characteristics of the protein before it bonds with octanal, it also describes the electronic characteristics after it has bonded. This shows exactly the kind of step change that the French team measured back in 2007.
That immediately opens up some interesting opportunities. With the ability to model and predict the electronic behaviour of this protein comes the ability to use it as a reliable component in more complex systems such as electronic circuits.
That’s what these guys mean by proteotronics—the ability to use proteins as reliable, well understood components, just like LEDs, transistors and the such like. The first application that they describe is the electronic nose—a device that can distinguish certain smells by the electronic signals generated by OR-17.
But this is just the beginning. Receptors are sensitive to a huge range of biomolecules so this opens up the possibility that they can be easily incorporated into the design of electronic systems in future.
Ref: arxiv.org/abs/1405.3840 : Proteotronics: Electronic Devices Based On Proteins