Hemostasis Thrombosis

Ludmila Bronstein PhD

Carolyn Turner

A major focus of our research is understanding the metal- and membrane binding properties of the vitamin K-dependent proteins that are critical for normal hemostasis and likely play a role in thrombosis. We are using fluorescence and NMR spectroscopy and x-ray crystallography to determine the mechanism of binding of vitamin K-dependent proteins to membranes.  We have recently developed a unique widefield and confocal intravital microscope that will enable studies of membrane binding of vitamin K-dependent proteins in vivo.  Vitamin K is a cofactor for a single known enzymatic reaction: the conversion of glutamic acid to gamma-carboxyglutamic acid, or Gla, on vitamin K-dependent proteins during their biosynthesis. Gla, a metal binding amino acid, confers metal binding properties on proteins and is required for protein-membrane interaction of vitamin K-dependent proteins.  Carboxylase activity is found in essentially all mammalian tissues and is widely distributed in vertebrates.  Recently carboxylase has been identified in invertebrates and the enzyme bears high sequence homology with mammalian carboxylase.  It is thus likely that this amino acid plays an important biological role in other protein functions. The biosynthesis and function of Gla is a major focus of research in this laboratory.  We are initiating efforts to identify novel Gla containing proteins that may have conserved function through multiple phyla.
 P-selectin, a molecule we discovered and originally called PADGEM, is a cell adhesion molecule that resides in the storage granules of platelets and endothelial cells. Upon cell stimulation, the protein is translocated to the plasma membrane where it functions as a leukocyte receptor for PSGL-1 on neutrophils and monocytes.  We are using our intravital microscopy facility, in conjunction with a variety of genetically modified mice, to explore the role of these adhesion molecules in inflammation and thrombosis in vivo.