Thursday, August 4, 2011

Evolution provides clue to blood clotting

A simple cut to the skin unleashes a complex cascade of chemistry to stem the flow of blood. Now, scientists at Washington University School of Medicine in St. Louis have used evolutionary clues to reveal how a key clotting protein assembles. The finding sheds new light on common bleeding disorders.


The long tube-shaped protein with a vital role in blood clotting is called von Willebrand Factor (VWF). Made in cells that form the inner lining of blood vessels, VWF circulates in the blood seeking out sites of injury. When it finds them, its helical tube unfurls to catch and form . Defects in VWF cause von Willebrand Disease, the most common inherited bleeding disorder in humans.


"The challenge for the cell is how to build this massive protein without clogging the machinery," says J. Evan Sadler, MD, PhD, professor of medicine and senior author of the study published in July in the . "The cell has solved this problem by making the assembly of von Willebrand Factor dependent on its location in the cell."


And VWF knows its location in a cell because pH, a measure of how acidic or basic a liquid is, varies from one to the next. On a scale of 0 to 14, pure water has a neutral pH of about 7; human blood is slightly basic with a pH of 7.4.


In a cell, the building blocks of VWF form in an area with the same pH as blood. Then these building blocks are shipped to an area that is more acidic. Called the Golgi, this cellular compartment is known for its role in packaging proteins and has a pH of about 6.2. In this acidic environment, the building blocks of VWF are able to form long chains and fold into its signature helical tubules. But how this assembly process works has not been well understood.


From basic biophysics, Sadler and his colleagues knew that only one amino acid in the long is likely to "sense" a pH change from 7.4 to 6.2. Moving to an acidic environment, this amino acid, histidine, gains a positive charge. The group suspected that this charge may trigger the VWF building blocks to link together in a long chain.


But there are many histidines located throughout the chain. Like 26 letters of the alphabet form thousands of words, 20 essential form all proteins in the body. To identify which histidines might be guiding the amino acid chain to form the long VWF tubules, Sadler and his team looked to evolution.


"If a particular histidine is important in this process, it should be present in the same location across many species," Sadler says.


So Sadler's group, including the paper's first author, Luke T. Dang, who was an undergraduate student when he did this work, gathered the DNA sequences of VWF for humans, 19 other placental mammals, a marsupial, two birds, a reptile, an amphibian and five fish. Dang is now a graduate student at the University of Washington, Seattle.


"By lining up the sequences, we found a relatively small number of histidines that are in the same place across species," Sadler says. "It then becomes manageable to mutate them individually and see if that prevents von Willebrand Factor from assembling."


Out of the many histidines in the amino acid sequence of VWF, they found two that are important in sensing the pH change and guiding the to form chains in an . When Dang replaced either of these histidines with an amino acid that provides no positive charge, the chain did not form. But when Dang forced a positive charge to always be present at these locations, the chain formed again.


"A positive charge at these positions is important for von Willebrand Factor to assemble properly so it can perform its biological function," says Sadler, also a hematologist who specializes in treating patients with blood clotting disorders. "Without VWF, you bleed."


According to Sadler, defects in VWF disproportionately affect women because the protein is especially important for controlling bleeding during menstruation and childbirth. Sadler says this work helps to better understand the defects in pathways that cause von Willebrand Disease and related conditions.


More information: Dang LT, Purvis AR, Huang RH, Westfield LA, Sadler JE. Phylogenetic and functional analysis of histidine residues essential for pH-dependent multimerization of von Willebrand Factor. Journal of Biological Chemistry. July 2011.


Provided by Washington University School of Medicine (news : web)

Researchers stumble on colorful discovery

Dr. Cathleen Crudden is shown here at work in her Queen's University (Ontario, Canada) lab with her rhodium research team including graduate student Eric Keske and postdoctoral fellow Dr. Olena Zenkina. Credit: Queen's University


Modified metals that change colour in the presence of particular gases could warn consumers if packaged food has been exposed to air or if there's a carbon monoxide leak at home. This finding could potentially influence the production of both industrial and commercial air quality sensors.


"We initially found out by accident that modified rhodium reacts in a colourful way to different ," says Cathleen Crudden, a professor in the Department of Chemistry. "That happy accident has become a driving force in our work with rhodium."


Rhodium that is modified using carbon, nitrogen or –based complexes changes to yellow in the presence of nitrogen, deep blue in the presence of oxygen, and brown in the presence of .


This colour change occurs because of the way that the gases bind to the compound's central metal, according to the researchers.


Another remarkable aspect of this discovery is that the chemical changes take place without disrupting the exact placement of each individual atom in the compound's crystalline lattice. Dr. Crudden notes that this type of transformation is virtually unprecedented.


Rhodium is the main metal used in the production of catalytic convertors to reduce the toxicity of car exhaust emissions. Dr. Crudden's team, including graduate student Eric Keske and postdoctoral fellow Dr. Olena Zenkina, is currently investigating whether cobalt, a significantly cheaper metal than , reacts similarly.


Provided by Queen's University (news : web)

New compounds for molecule interferometry experiments

 

When waves meet, a new single wave is created. This phenomenon is well understood for mechanical waves such as sound, and electro-magnetic waves such as light, and the "interference" of light waves is applied in astronomy, fiber optics, and oceanography. The observation that even individual large organic molecules can delocalize over large distance and interfere—not with each other, but each one with itself—is rather new, and its study requires suitable substances.


A team of chemists led by Marcel Mayor at the Universit├Ąt Basel has recently designed a new series of compounds that were successfully used for interferometry experiments by a group of experimental physicists headed by Markus Arndt at the Universit├Ąt Wien, as they report in the European Journal of Organic Chemistry.


Chemical functionalization allows the properties of the molecules to be tailored to the needs of the experiments. To be compatible with interferometry, compounds must be highly volatile, stable, and easily ionized. In order to understand the transition between quantum and classical mechanics, it is important to study molecules of increasing mass. The first two criteria can be met by highly fluorinated compounds. To meet the requirements of a high molecular mass and good detectability, the authors judiciously paired the fluorinated moieties to a porphyrin core.


The team presented a modular synthesis of seven fluorinated porphyrins. The aim of the authors was to cover a specific mass range and to optimize the design of the structures towards high volatility; their resulting synthetic strategy is straightforward and easily applied. The fluorine components are coupled to the outer parts of the porphyrins in the last step of the synthesis. They can thus be easily modified to fine-tune the interferometry experiments. Despite the high fluorine content of the porphyrins, these compounds could still be produced by established organic synthesis protocols.


The researchers showed that at least one of their prepared met the criteria for thermal evaporation and stability, and the team plans to adopt the modular synthesis technique reported for the design of more specific, mass-limited, sublimable organic dyes for future molecule interferometry experiments.


More information: Marcel Mayor et al., Highly Fluorous Porphyrins as Model Compounds for Molecule Interferometry, European Journal of Organic Chemistry, http://dx.doi.org/ … oc.201100638


Provided by European Journal of Organic Chemistry

Spider silk glue inspires next-generation technology

 Water affects orb spider web glue differently than cobweb glue. Orb web glue reacts to humidity, but cobweb glue resists it. These findings by a University of Akron research team inspire the development of new materials according to how they respond to stimuli.


This newly released research by Vasav Sahni, a UA polymer science graduate student; Todd Blackledge, the Leuchtag Endowed Chair and associate professor of biology and integrated bioscience; and Ali Dhinojwala, UA Department of Polymer Science chair and H. A. Morton Professor of Polymer Science, is published in the July 21, 2011, issue of Scientific Reports.


Humidity triggers adaptability


The research shows that the sticky that coats the silk threads orb-weaving spiders spin has a different structure, property makeup and response to humidity than glues produced by their evolutionary descendants, cobweb-weaving spiders. The cobweb spider's gumfoot glue acts as a viscoelastic liquid that is resistant to changes in humidity, consequently maintaining constant elasticity and adhesion.


Orb weavers, on the other hand, produce glue that acts like a viscoelastic solid. Highly humidity-sensitive, this glue expands in magnitude and demonstrates a monotonous increase in elasticity under increased humidity. The glue also displays a decrease in surface adhesion that results in optimal adhesion at intermediate humidity.


"We suggest that observed differences are due to different 'tackifiers' used in these systems," says Sahni. "These results will inspire future efforts in fabricating stimuli-resistant and stimuli-sensitive materials."


Evolutionary changes advance science


Behaviors of natural biomaterials, such as spider glue responses to humidity, provide templates for developing and devices that change dimension, property makeup and function in response to external stimuli, according to Vasav. He adds that provide powerful tools to advance biomimetic research toward understanding key elements that control biomaterials' environmental responsiveness or resistance to stimuli.


The researchers probed individual glue droplets to reach their findings. They explain in their paper that "both orb web and cobweb spiders depend on viscid glue droplets for their silk to adhere to insect prey. Both types of spiders use the same sets of glands to produce the adhesive." However, similarities between the two, for the most part, end there.


The opposite reactions of the two bioadhesives to humidity are as dramatic as the complexity of processes contributing to these phenomena, the scientists explain in their research. Consequently, the researchers designed a polymer model of the glue droplet, dissolved in water, to simplify and better understand the underlying mechanisms that cause the orb web spiders' silk adhesive to react to humidity.


Reactions of spider glue, pine cones, bird feathers, and several other natural materials to different stimuli provide scientists inspiration for developing next-generation materials based on biomimetic research, or research that mimics nature.


More information: See "Changes in the Adhesion Properties of Spider Aggregate Glue During the Evolution of Cobwebs."


Provided by University of Akron