The structure and functions are closely interrelated

Proteins are the building material for all living things, and there is in fact an unlimited variety of their species, most of the very complex structures of which have not yet been determined. These structures can be the key to the development of new medicines or to understand the basic biological processes.  

But to clarify the structure of atoms in these complex folded molecules, it is usually required that they form crystals large enough to be studied in detail, and for many proteins it is either impossible or extremely difficult.

At present, a new method developed by researchers from the Massachusetts Institute of Technology (MIT) and other organizations is very promising for obtaining images of individual proteins with very high resolution, despite how complex their structure may be, and not The need for crystallization. The results are described in the Physical Review by Ashok Ajoy, a graduate student of MIT, research fellow Ulf Bissbort, associate professor of nuclear physics and technology Paola Cappellaro and other scientists from the Massachusetts Institute of Technology, the Singapore University of Technology And Design (Singapore Univ. Of Technology and Design) and Harvard University.

This method uses microscopic defects inside the crystal structure of the diamond - defects that can be introduced in a controlled manner under laboratory conditions. These defects, called nitrogen-vacant vacancies or NV-centers (nitrogen-vacancy, NV), arise when nitrogen atoms are introduced into the crystal structure, each replacing one carbon atom in an ideal lattice of diamond.

Such lattices can also include natural nitrogen-substituted vacancies-flaws, when the carbon atom is absent in its usual place in the lattice. When a nitrogen atom and a vacancy occur, they form an NV center, which can be used to detect positions and properties - in particular, spin states - of photons and electrons in atoms located in close proximity to it.

This is achieved by translucent laser light, which causes the fluorescence of nitrogen-substituted vacancies. By registering and analyzing the emitted light, you can reconstruct the details of the spin of nearby particles.

The opportunity to use NV centers in diamond has appeared in the last few years, says Ajoy, and many groups are now working to use them for applications in quantum computing and quantum communication. When NV-centers are located close to the surface of a diamond-in several nanometers-they can also be used to trap the spin states of particles in a molecule placed on a surface. Then, in principle, it is possible to detect and map individual atoms and their position, revealing the structure of the molecule.

The idea is to "place a biological molecule on a diamond and try to determine its structure," explains Ajoy. In proteins, "the structure and functions are closely interrelated," he says, so the ability to accurately map this structure can help in understanding how certain basic biological processes occur and how new drugs can be developed that can interact with specific molecular targets.

"This can help in developing what is suitable for placement on or near the [target molecule], or to block it," says Ajoy. "The first step is to know the structure."

Attempts to decipher the structure of the protein molecule were mainly based on X-ray crystallography, transmission electron microscopy or nuclear magnetic resonance. But for all these methods large volumes of the sample are required - for example, for X-ray diffraction, aggregation of molecules in the form of crystals is required, so none of them can be used to study individual molecules. This greatly limits the possibility of using such methods.

"There are many molecules in which this does not work, because it is impossible to grow crystals or they are very difficult to grow," says Ajoy. "For these molecules, our method can be useful, because you do not need crystals, you just need a molecule."

http://www.rdmag.com/news/2015/02/diamonds-could-help-bring-proteins-focus