Welcome to the Majumder Lab
The studies in the Majumder laboratory center on the molecular mechanisms that are responsible for maintaining normal hemostasis. In particular, our research focuses on the structure-function relationships of plasma coagulants and anticoagulants. Currently, the lab is pursuing research in the following areas: 1) determining the physiological role of an important plasma glycoprotein, Protein S (PS), and 2) capitalizing on our discovery of a novel regulatory function of PS towards Factor IXa to test whether inhibiting PS will mitigate the Hemophilia B that results from a deficiency or misregulation of Factor IXa and to test whether PS will ameliorate disorders due to hyperactive Factor IXa.
Our research utilizes a wide spectrum of experimental approaches and methodology, including molecular modeling, creation of mutant proteins, protein-protein interaction assays, blood clotting assays, and animal models.
PS is a vitamin K-dependent plasma glycoprotein synthesized in the endothelium. PS deficiency is one of several risk factors for thrombophilia, and PS deficiency can increase the risk of abnormal blood clotting such as Deep Vein Thrombosis and Pulmonary Embolism. In severe cases of PS deficiency, soon after birth, infants develop a life-threatening blood clotting disorder called purpura fulminans. Despite its critical importance as an anticoagulant, 30 years of study by others failed to reveal the exact role of PS in blood coagulation. We recently discovered a previously unknown role of Protein S in regulating the clotting factor IXa, i.e., thrombin generation via Factor IXa is inhibited by Protein S. [This work was featured on the cover of the October, 2012 issue of Arteriosclerosis, Thrombosis, and Vascular Biology; see below].
Copyright © 2012 by American Heart Association, Inc.
The inhibition of thrombin generation via Factor IXa by Protein S is being exploited to more effectively treat Hemophilia B. Hemophilia B results from a deficiency in Factor IXa. Factor IXa converts prothrombin to thrombin, which forms the blood clot at an injured site. Hemophilia B is treated by infusion of Factor IXa to replace the missing or inactive Factor IXa in affected individuals. However, the infused Factor IXa has a limited therapeutic lifetime, likely in part, because it is inhibited by Protein S. Thus, our studies are directed towards developing agents that inhibit the activity of Protein S. Such agents are expected to increase the therapeutic efficacy of Factor IXa replacement therapy for Hemophilia B patients. We are using mouse models to assess whether one inhibitor of Protein S, i.e., a specific Protein S antibody, prolongs Factor IXa therapy. In addition, we are collaborating with Dr. Bruce Sullenger (Duke University) to produce oligonucleotide aptamers that inhibit PS activity with high affinity and specificity. Aptamer-mediated inhibition of PS is preferred over antibody-based inhibition because aptamers have low or no immunogenicity compared with proteins, aptamers are substantially easier to synthesize in large, chemically pure quantities, aptamer-target stoichiometries and affinities are easily measured to determine appropriate drug doses, and, unlike proteins, aptamers can be easily modified chemically to enhance their plasma lifetimes.
Overview of Selex Process which is used to create Aptamers
We are taking an opposite approach with PS to develop treatments for thrombosis, diseases that result form inappropriate activation of blood coagulation. For example, thrombophilia is an X-linked disorder that results from hyperactive Factor IXa. We are investigating the precise mechanism by which PS inhibits Factor IXa with the goal of creating more effective PS-based inhibitors to alleviate thrombophilia and other hypercoagulation disorders. In order to determine the mechanism we are trying to determine binding sites in FIXa that would bind Protein S.
FIXa showing hydrophobic surfaces:
Summary: Protein S has been the subject of research by numerous investigators for over 30 years. However, the published studies have been contradictory and confusing regarding the true function of Protein S in blood coagulation. Importantly, we have been able to creatively avoid artifacts of experimental design that we discovered to have plagued many earlier studies. Thus, our work will further clarify the biochemistry and physiology of Protein S, and our findings will have direct applications in creating new antithrombotic drugs and agents to ameliorate Hemophilia.