Another piece of the ion pump puzzle

V-ATPases consist of a so-called ‘V complex’, which transfers energy derived from ATP hydrolysis into rotational motion, thereby promoting ion transport through to the membrane-bound V0 complex. These two complexes are joined by three ‘stalks’, including a central stalk composed of subunits named D and F, although this segment of the protein is poorly characterized. “The structure of this central axis of V-ATPase has not been obtained,” says Takeshi Murata of the RIKEN Systems and Structural Biology Center in Yokohama, “and we believe such structural studies are very important to understand this protein’s precise mechanism.”

Murata and colleagues recently succeeded in obtaining high-resolution structural information about the DF complex of V-ATPase obtained from the bacteria Enterococcus hirae1. By comparing this structural information against an equivalent segment from F-ATPase, which synthesizes rather than hydrolyzes ATP, the researchers were able to identify functional domains that may be specifically required by V-ATPases.

They determined that the E. hirae D subunit is composed of a pair of long helical structures coiled around each other, with a short hairpin-shaped loop at one end. According to Murata, the discovery of this latter structure was unexpected. “This short beta-hairpin region is a unique structure, although the rest of the D structure is very similar to that of other rotary complexes such as F-ATPase and flagellar motors,” he says. This segment does not appear to be essential for V-ATPase assembly, but ATP processing efficiency was reduced when the researchers deleted this hairpin from the subunits.

In contrast, the E. hirae F subunit assumed a more compact structure, relatively similar to its A- and F-ATPase counterparts; the researchers determined that it specifically associates with the middle portion of the D subunit’s coiled helical segment, an interaction that depends heavily on a particular helix within the F subunit. 

Although untangling this structure represents a major step forward, this complex must also be understood as part of a far larger entity (Fig. 1). Murata and colleagues have already begun tackling this. “We recently succeeded at solving the structure of V1-ATPase with a resolution of 2.1 Angstroms,” says Murata, “and we are now preparing this manuscript for publication.”

More information: Saijo, S.,et al. Crystal structure of the central axis DF complex of the prokaryotic V-ATPase. Proceedings of the National Academy of Sciences USA 108, 19955–19960 (2011).

Provided by RIKEN (news : web)

Neutrons answer shampoo formulation puzzle

A research team at the Institut Laue-Langevin, the flagship centre for neutron science, has demonstrated quantitatively the science behind an anomaly in the surface tension of polyelectrolyte/surfactant mixtures. Their findings show that the dramatic increase in surface tension that affects the production of various pharmaceutical and cosmetic formulations is caused by the comprehensive aggregation of active ingredients. They have outlined a way to reload interfaces with functional components simply by tuning the way the materials are handled.

Surface tension is a property of liquids resulting from the cohesion of their molecules that helps them resist an external force. It is responsible for the shape of liquid droplets and the reason why insects can run on the surface of ponds.

Surfactants are substances that lower the surface tension of a liquid and can capture other substances, such as oil or grease in cleaning products. They are often combined with polyelectrolytes, made of long charged molecules, to improve the efficiency of detergents, wetting agents, emulsifiers, foaming agents, and dispersants in paints, shampoos and conditioners, and are used throughout the food industry. Also, the strong attractive interactions of surfactants with natural polyelectrolytes, such as proteins or DNA, play an important role in many biological processes, as well as in medical applications, such as drug and gene delivery.

The commercial production and performance of polyelectrolyte/surfactant mixtures, however, is affected by a peculiar phenomenon, first investigated in depth a decade ago. Whilst adding a surfactant to a polyelectrolyte solution initially causes the surface tension to decrease, as further surfactant is added the surface tension dramatically increases again. This feature, known as a ‘cliff edge peak’, is accompanied by a change in the appearance of the mixture, with the eventual loss of the cloudiness that is present as soon as the materials first interact.

From an industrial production point of view, this rise in surface tension reduces the performance of the additive, often requiring the introduction of further surfactant at extra cost. As a result, there is a lot of interest in understanding the interactions between these mixtures at the atomic level both in solutions and at surfaces. Of particular interest are the primary causes of the cliff edge peak and ways to prevent, lessen or delay its effects that could lead to more efficient formulations and reduce the effects of many pollutants in our environment.

To investigate this problem, Dr Richard Campbell (Institut Laue-Langevin), Dr Imre Varga (Eötvös-Loránd University, Hungary) and their co-workers looked at a system studied widely in the literature – an oppositely charged poly (diallyldimethylammonium chloride)/sodium dodecyl sulfate (Pdadmac/SDS) system.

The international research team, which also includes members from the UK and Sweden, used neutron reflectometry, a reflection technique used for measuring the composition and structure of thin films, to monitor the surface properties with respect to the slow generation of the cliff edge peak. The instrument used was the brand new FIGARO reflectometer (Fluid Interfaces Grazing Angles ReflectOmeter) at the Institut Laue-Langevin, which was constructed during the Institute’s innovative Millennium Programme. The researchers showed quantitatively for the first time that this striking feature in the surface tension results from the slow precipitation of particles into sediment from the aqueous solution. The precipitation depletes the solution and consequently the surface of its active ingredients, and also accounts for the loss of cloudiness observed.

As well as uncovering the reasons behind the rise in surface tension, the team were also keen to investigate methods to prevent its impact, which could directly benefit commercial applications. In the literature, researchers have suggested that the way these mixtures are handled could affect the nature of the material in the solution - a phenomenon called “non-equilibrium effects”.

To test whether the re-dispersion of surface-active material could actually switch off the cliff edge peak effect, the team carefully agitated a series of mixtures after the settling process had finished. A small mechanical stress provided just enough energy to re-disperse some of the sedimented particles and re-supplied the air/liquid interface with enough material to lower the surface tension once again.

“By approaching the problem in a different way, we have shown that the way you handle polyelectrolyte/surfactant systems can produce a variety of tuneable surface properties,” says Dr. Richard Campbell. “We hope that our findings will allow future industrial chemists across the pharmaceutical, detergency and cosmetic industries to generate better product output from their raw materials by learning to handle them in a smarter way, and create optimum surface properties on demand, rather than simply buying in more material to improve performance.”

There is hope also that this work can lead on to novel drug or gene delivery applications where one could apply an external stimulus to a stable biomacromolecule system in order to trigger the delivery of proteins or DNA to a given target.

More information: Re.:J. Phys. Chem. B, Article ASAP, DOI: 10.1021/jp2088803

Provided by Institut Laue-Langevin

Engineers solve energy puzzle: How energy levels align in a critical group of advanced materials

 University of Toronto materials science and engineering (MSE) researchers have demonstrated for the first time the key mechanism behind how energy levels align in a critical group of advanced materials. This discovery is a significant breakthrough in the development of sustainable technologies such as dye-sensitized solar cells and organic light-emitting diodes (OLEDs).

Transition metal oxides, which are best-known for their application as super-conductors, have made possible many sustainable technologies developed over the last two decades, including organic photovoltaics and organic light-emitting diodes. While it is known that these materials make excellent electrical contacts in organic-based devices, it wasn't known why -- until now.

In research published in Nature Materials, MSE PhD Candidate Mark T. Greiner and Professor Zheng-Hong Lu, Canada Research Chair (Tier I) in Organic Optoelectronics, lay out the blueprint that conclusively establishes the principle of energy alignment at the interface between transition metal oxides and organic molecules.

"The energy-level of molecules on materials surfaces is like a massive jigsaw puzzle that has challenged the scientific community for a very long time," says Professor Lu. "There have been a number of suggested theories with many critical links missing. We have been fortunate to successfully build these links to finally solve this decades-old puzzle."

With this piece of the puzzle solved, this discovery could enable scientists and engineers to design simpler and more efficient organic solar cells and OLEDs to further enhance sustainable technologies and help secure our energy future.

Story Source:

The above story is reprinted from materials provided by University of Toronto Faculty of Applied Science & Engineering.

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

Journal Reference:

Mark T. Greiner, Michael G. Helander, Wing-Man Tang, Zhi-Bin Wang, Jacky Qiu, Zheng-Hong Lu. Universal energy-level alignment of molecules on metal oxides. Nature Materials, 2011; DOI: 10.1038/nmat3159

Foldit Online Protein Puzzle

Inside your cells, proteins allow your body to break down food to power your muscles, send signals through your brain that control the body, and transport nutrients through your blood. Every protein consists of a long chain of joined-together amino acids, which are small molecules made up of atoms of carbon, oxygen, nitrogen, sulfur and hydrogen. Small proteins can consist of 100 amino acids, whereas some human proteins are much larger, with thousands of amino acids.

Each type of protein folds up into a very specific shape, which specifies the protein's function. The Foldit exploration puzzle game attempts to predict the structure of a protein by taking advantage of our puzzle-solving intuitions and having people play competitively to fold the best proteins. Players can also design brand new proteins that could help prevent or treat important diseases.

Another objective of the project is to find new proteins that can help in turning plants into fuel. For this to happen plant material must be broken down (this is currently done by microbial enzymes—proteins—called "cellulases").

This game is a product of a collaboration between University of Washington Departments of Computer Science & Engineering and Biochemistry.

See more projects in Free,  Data Processing,  All Ages.