A fibrin fiber, roughly 100 nanometers in diameter (or 10 million times smaller than a millimeter) is stretched by the tip of an atomic-force microscope (not visible here). Image by Michael R. Falvo; ©2007 Endeavors; click to enlarge.
Super-strong Proteins in Clots
by Jan McColm
Scientists used to think that a blood clot got its strength from a weave of protein strands — much as a woven rug is stronger than its individual threads. But new research at UNC has shown that the strands of the individual protein that make up a clot — fibrin — are one of the strongest proteins ever measured. And what’s more, they are elastic.
“It was extraordinary,” says Susan Lord, professor of pathology and laboratory medicine, and one of the lead authors on the study. On average, the researchers could stretch an individual fibrin strand more than four times its original length before it broke. The strands could bounce back to their original shape even after being stretched out to three times their length.
The team from UNC and Wake Forest University developed a new way to measure the stretched protein. The researchers suspended a fluorescently colored fibrin strand over a microscopic groove in a glass plate. Then they pulled the tip of an atomic-force microscope through the groove, and recorded the changes in length and elasticity of the fibrin strand using a fluorescence microscope.
Turns out that fibrin is stronger than spiders’ silk. That means it’s great for stopping bleeding and healing a cut. But in heart disease, blood clots form inside your blood vessels — the last place you’d want them. Tough clots make heart disease prevention and treatment difficult.
Current treatments use clot-busting drugs such as tissue plasminogen activator, or tPA, which attacks the fibrin fibers directly and chops them up. “Our study suggests that this is a good treatment for heart disease because it’s the fibrin fibers that are so strong, and if you can break the fibers then you can break the clot and restore the blood flow,” Lord says.
But some people don’t respond at all to tPA, and others respond too much — their blood stops clotting altogether. Lord says we need more investigations to solve these problems. But just knowing more about fibrin and how it strengthens clots will give her plenty of new avenues to explore.
The study was published in the August 4 edition of the journal Science. Martin Guthold, also a lead author on this study, carried out his graduate work at UNC and is now an assistant professor of physics at Wake Forest. Other UNC authors are Louise Jawerth, now a doctoral candidate in physics at Harvard University; Richard Superfine, Bowman and Gordon Gray Professor of Physics; and Mike Falvo, research assistant professor in the Curriculum in Applied and Materials Sciences.
