Navigation Links
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 platelets and form blood clots. 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 Journal of Biological Chemistry. "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 cellular structure 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 protein chain 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 amino acids 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 building blocks to form chains in an acidic environment. 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.


Contact: Julia Evangelou Strait
Washington University School of Medicine

Related medicine news :

1. Genetic map of African-Americans to aid study of diseases, human evolution
2. UCSF-led team decodes evolution of skin and ovarian cancer cells
3. Scientists identify a novel mechanism for evolution of highly aggressive cancers
4. Evolutionary geneticist to give talk at UC Riverside on how biological species evolve and adapt
5. Single Gene Linked to Evolution of Human Brain
6. Center to revolutionize chemical manufacture is open for business
7. Polygamy hurt 19th century Mormon wives evolutionary fitness
8. Study looks into evolution of breast cancer in Spain
9. Punctuated evolution in cancer genomes
10. UH biochemist works to revolutionize ovarian cancer treatment
11. Biologists, educators recognize excellence in evolution education
Post Your Comments:
Related Image:
Evolution provides clue to blood clotting
(Date:6/25/2016)... Beach, CA (PRWEB) , ... June 25, 2016 , ... ... UCLA with Magna Cum Laude and his M.D from the David Geffen School of ... Diego and returned to Los Angeles to complete his fellowship in hematology/oncology at the ...
(Date:6/25/2016)... ... 25, 2016 , ... On Friday, June 10, Van Mitchell, Secretary of the ... to iHire in recognition of their exemplary accomplishments in worksite health promotion. , The ... Health & Wellness Symposium at the BWI Marriott in Linthicum Heights. iHire was one ...
(Date:6/24/2016)... , ... June 24, 2016 , ... A recent ... most people are unfamiliar with. The article goes on to state that individuals are ... many of these less common operations such as calf and cheek reduction. The Los ...
(Date:6/24/2016)... ... June 24, 2016 , ... June 19, 2016 is World Sickle Cell Observance ... and the benefits of holistic treatments, Serenity Recovery Center of Marne, Michigan, ... Disease. , Sickle Cell Disease (SCD) is a disorder of the red blood cells, ...
(Date:6/24/2016)... Texas (PRWEB) , ... June 24, 2016 , ... ... International Conference and Scientific Sessions in Dallas that it will receive two significant ... of the grants came as PHA marked its 25th anniversary by recognizing patients, ...
Breaking Medicine News(10 mins):
(Date:6/23/2016)... VIEW, Calif. , June 23, 2016 ... a.m. CST on Thursday, July 7, 2016 , , , ... ) , , , , EXPERT PANELISTS:  , ... Nitin Naik; Senior Industry Analyst, Christi Bird; Senior Industry Analyst, Divyaa ... The global pharmaceutical industry is witnessing an ...
(Date:6/23/2016)... June 23, 2016  Guerbet announced today that it ... Supplier Horizon Award . One of 12 ... recognized for its support of Premier members through exceptional ... excellence, and commitment to lower costs. ... recognition of our outstanding customer service from Premier," says ...
(Date:6/23/2016)... YORK , June 23, 2016 ... waters, but it continues to present great opportunities to ... companies for today: Intrexon Corp. (NYSE: XON ... Arena Pharmaceuticals Inc. (NASDAQ: ARNA ), and ... more about these stocks and receive your complimentary trade ...
Breaking Medicine Technology: