Researchers used the X-ray crystallography method to obtain the first ever image of the protein prothrombin (one of the blood clotting factors). The flexible structure of the protein is a key factor in the development of blood clotting.
![Using X-ray crystallography, researchers at St. Louis University have published the first ever image of the important blood clotting protein known as prothrombin (coagulation factor II). The flexible structure of the protein is a key component in the development of blood clotting. [Courtesy of Saint Louis University].](https://www.hayadan.org.il/images/content3/2014/07/Prothrombin_400.jpg)
In results recently published in the scientific journal Proceedings of the National Academy of Sciences (PNAS), scientists from St. Louis University discovered that removing disordered segments from the protein structure reveals the molecular mechanism of a key reaction that initiates blood clotting. Researcher Enrico Di Cera, a physician trained in the Department of Biochemistry and Molecular Biology at St. Louis University, studies the substance thrombin, a vitamin K-dependent protein that facilitates blood clotting, and its inactive precursor prothrombin (or coagulation factor II).
"Prothrombin is essential for life and is the most important clotting factor," the researcher points out. "We are proud to report that our lab has finally been able to crystallize the prothrombin protein for the first time ever." Blood coagulation ensures our survival by preventing blood loss after injury. However, when coagulation is activated under inappropriate circumstances, it can lead to exhaustion and even fatal conditions such as heart attacks, strokes or deep vein thrombosis (a blood clot in the deep veins of the leg that can cause a life-threatening embolism in the lungs).
Before thrombin becomes active, it flows in our blood circulation in its inactive form (zymogen) known as prothrombin (pre-thrombin). When the active enzyme is needed (after a blood vessel injury, for example) the coagulation system starts to work and the prothrombin is converted to the active enzyme thrombin which causes the blood to clot.
X-ray crystallography is one of the tools scientists have that helps them understand processes at the molecular level. It allows a way to obtain a "frozen image" of the protein structure. As part of this method, scientists "grow" crystals of the protein they wish to study, "shoot" a beam of X-rays at it and record the data obtained as to how the rays disperse following their impact on the crystal. In the next step, they use computer software to create an image of the XNUMXD structure of the protein based on this data. Once scientists have the spatial picture of the molecule's structure, they can try and begin to understand how the protein works and how it reacts with other molecules in the body, or with drugs, for example.
Last year, the research team first published the XNUMXD structure of prothrombin. This primary structure lacks a part that is responsible for the activity with the membranes and other parts of it were not deciphered with the help of the method. Despite the fact that the researchers were able to crystallize the protein, it still had distorted regions that they could not observe. Inside the prothrombin there are two parts (circular segments) connected together by one author who intrigued the researchers due to the disorder inherent in it. "After we removed this segment, we were able to synthesize the protein in a few days, instead of months, while discovering for the first time the exact internal structure of the protein as a whole," notes the lead researcher.
In addition to this discovery, the researchers also discovered that the truncated version of prothrombin is converted to the active form of thrombin much faster than the codman. The structure lacking the twisted linker is actually the optimal form that converts to thrombin, and this reveals important information regarding the activity of prothrombin. For four decades scientists have been trying to synthesize the pro-thrombin protein - without success so far. "It took us almost two years to understand that the twisted connector is the key to this," explains the lead researcher.
"In the end, prothrombin revealed to us its secrets, and subsequently the molecular mechanism of a key reaction in blood coagulation, which will allow researchers in the field to design more effective drugs."
