My research interest involves structural and functional studies of membrane proteins, originating from prokaryotic and eukaryotic organisms, using x-ray crystallography. Membrane proteins mediate the cell exchange of energy, nutrients and information and, thus, are targets for a majority of the prescribed drugs (50% of drugs on the market target membrane proteins). Although, 25% of the proteins in genomes are membrane proteins, less than 1% of their structures are known. I am typically interested in secondary transport proteins among membrane proteins. They are highly relevant to human physiology and disease (eg. depression, diabetes, multidrug resistance). Also of note, at least two widely prescribed drugs [fluoxetine (Prozac) and omeprazole (Prilosec)], are targeted to membrane-transport proteins. Despite the utter medical importance of membrane proteins, the molecular basis of their function has been and continues to be an arduous task. Since the study of membrane proteins is challenging, the chances of success can be increased with the number of trials, specifically by implementing high throughput methodology in protein expression and crystallization.
- Carbohydrate transporters
Carbohydrates serve as basic fuel molecules for eukaryotic cells. These molecules are unable to freely diffuse across cellular membranes but instead require transporter proteins to either enter or exit cells. Carbohydrate transporters have similar structures, consisting of 12 transmembrane helixes. Aberrant transporter genes are the cause of several congenital defects of sugar metabolism (GLUT1 deficiency and Fanconi-Bickel syndromes), and a malfunction of glucose transporter expression or regulation (GLUT4) appears to contribute to the insulin resistance syndrome. In animal models of type II non-insulin dependent diabetes, a decrease in the levels of GLUT2 in the pancreatic cells precedes the development of diabetes. Homologous proteins of human GLUT were crystallized (see BMB website) and the structural determination is ongoing.
Proteins are dynamic systems and in order to understand the molecular basis of their function, it is important to determine the structures of several of their different key conformations. For example, below movie of Fructose-1,6-bisphosphatase (FBPase; a key gluconeogenic cytosolic phosphatase) represented the changes in protein conformation as it goes through the apo, substrates-, intermediate-, and product-bound states. The FBPase crystal structures in these different ligation stages were solved.
The movie of Lactose permease (the membrane transporter for lactose) also represented different stages of the protein action, however, currently, only one conformation is known. The dynamics shown in the movie is based on electron spin resonance studies corroborated with the available crystal structure showing the distance changes between specific spin labels in dynamic domains while the protein is transporting lactose.