Nanotechnology: Nanomechanical measurements of unprecedented resolution made on protein molecules

UCLA physicists have made nanomechanical measurements of unprecedented resolution on protein molecules.

The new measurements, by UCLA physics professor Giovanni Zocchi and former UCLA physics graduate student Yong Wang, are approximately 100 times higher in resolution than previous mechanical measurements, a nanotechnology feat which reveals an isolated protein molecule, surprisingly, is neither a solid nor a liquid.

"Proteins are the molecular machines of life, the molecules we are made of," Zocchi said. "We have found that sometimes they behave as a solid and sometimes as a liquid.

"Solids have a shape while liquids flow -- for simple materials at low stresses. However, for complex materials, or large stresses, the behavior can be in-between. Subjected to mechanical forces, a material might be elastic and store mechanical energy (simple solid), viscous and dissipate mechanical energy (simple fluid), or visco-elastic and both store and dissipate mechanical energy (complex solid, complex fluid). The viscoelastic behavior characteristic of more complex matter had not been clearly seen before on isolated proteins because mechanical measurements tend to destroy the proteins."

Zocchi and Wang's new nanotechnology method allowed them to apply stresses and probe the mechanics of the protein without destroying it. Wang, now a physics postdoctoral fellow at the University of Illinois in Urbana-Champaign, and Zocchi discovered a "transition to a viscoelastic regime in the mechanical response" of the protein.

"Below the transition, the protein responds elastically, like a spring," Zocchi said. "Above the transition, the protein flows like a viscous liquid. However, the transition is reversible if the stress is removed. Functional conformational changes of enzymes (changes in the shape of the molecule) must typically operate across this transition."

The measurements were performed on the enzyme guanylate kinase, or GK, a member of an essential class of enzymes called kinases. Specifically, GK transfers a phosphate group from ATP (the universal "fuel" of the cell) to GMP, producing GDP, an essential metabolic component, Zocchi said.

The study on the characterization of the "visco-elastic transition" is reported this month in the online journal PLoS ONE, a publication of the Public Library of Science. The research was federally funded by the National Science Foundation's division of materials research and by a grant from the University of California Lab Research Program.

Zocchi and Wang published related findings earlier this year in the journal Europhysics Letters, a publication of the European Physical Society, and the journal Physical Review Letters.

In previous research, Zocchi and colleagues reported a significant step in controlling chemical reactions mechanically last year, made a significant step toward a new approach to protein engineering in 2006, created a mechanism at the nanoscale to externally control the function and action of a protein in 2005, and created a first-of-its-kind nanoscale sensor using a single molecule less than 20 nanometers long in 2003. A nanometer is roughly 2,000 times smaller than the width of a human hair.

The above story is reprinted from materials provided by University of California - Los Angeles. The original article was written by Stuart Wolpert.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Yong Wang, Giovanni Zocchi. Viscoelastic Transition and Yield Strain of the Folded Protein. PLoS ONE, 2011; 6 (12): e28097 DOI: 10.1371/journal.pone.0028097

Note: If no author is given, the source is cited instead.

3-D nanoparticle in atomic resolution

In chemical terms, nanoparticles have different properties from their "big brothers and sisters:" They have a large surface area in relation to their tiny mass and at the same time a small number of atoms. This can produce quantum effects that lead to altered material properties. Ceramics made of nanomaterials can suddenly become bendy, for instance, or a gold nugget is gold-coloured while a nanosliver of it is reddish.

New method developed

The chemical and physical properties of nanoparticles are determined by their exact three-dimensional morphology, atomic structure and especially their surface composition. In a study initiated by ETH Zurich scientist Marta Rossell and Empa researcher Rolf Erni, the 3D structure of individual nanoparticles has now successfully been determined on the atomic level. The new technique could help improve our understanding of the characteristic of nanoparticles, including their reactivity and toxicity.

Gentle imaging processing

For their electron-microscopic study, which was published recently in the journal Nature, Rossell and Erni prepared silver nanoparticles in an aluminium matrix. The matrix makes it easier to tilt the nanoparticles under the electron beam in different crystallographic orientations whilst protecting the particles from damage by the electron beam. The basic prerequisite for the study was a special electron microscope that reaches a maximum resolution of less than 50 picometres. By way of comparison: the diameter of an atom measures about one Angström, i.e. 100 picometres.

To protect the sample further, the electron microscope was set up in such a way as to also yield images at an atomic resolution with a lower accelerating voltage, namely 80 kilovolts. Normally, this kind of microscope -- of which there are only a few in the world -- works at 200 -- 300 kilovolts. The two scientists used a microscope at the Lawrence Berkeley National Laboratory in California for their experiments. The experimental data was complemented with additional electron-microscopic measurements carried out at Empa.

Sharper images

On the basis of these microscopic images, Sandra Van Aert from the University of Antwerp created models that "sharpened" the images and enabled them to be quantified: the refined images made it possible to count the individual silver atoms along different crystallographic directions.

For the three-dimensional reconstruction of the atomic arrangement in the nanoparticle, Rossell and Erni eventually enlisted the help of the tomography specialist Joost Batenburg from Amsterdam, who used the data to tomographically reconstruct the atomic structure of the nanoparticle based on a special mathematical algorithm. Only two images were sufficient to reconstruct the nanoparticle, which consists of 784 atoms. "Up until now, only the rough outlines of nanoparticles could be illustrated using many images from different perspectives," says Marta Rossell. Atomic structures, on the other hand, could only be simulated on the computer without an experimental basis.

"Applications for the method, such as characterising doped nanoparticles, are now on the cards," says Rolf Erni. For instance, the method could one day be used to determine which atom configurations become active on the surface of the nanoparticles if they have a toxic or catalytic effect. Rossell stresses that in principle the study can be applied to any type of nanoparticle. The prerequisite, however, is experimental data like that obtained in the study.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Swiss Federal Laboratories for Materials Science and Technology (EMPA). The original article was written by Simone Ulmer/ETH Life.

Journal Reference:

Sandra Van Aert, Kees J. Batenburg, Marta D. Rossell, Rolf Erni, Gustaaf Van Tendeloo. Three-dimensional atomic imaging of crystalline nanoparticles. Nature, 2011; 470 (7334): 374 DOI: 10.1038/nature09741