Vince J. LiCata

Associate Professor
Ph.D., Johns Hopkins University, 1990
Protein structure and function; extremophilic proteins; protein-DNA interactions; protein-lipid interactions.

licata@lsu.edu


LiCata Lab Homepage


Our laboratory studies proteins: most particularly protein-DNA and protein-ligand interactions, along with protein folding and stability. Our work is primarily focused on the energetics and global structural attributes of these processes and how they are controlled. We utilize several different model systems to address questions in these areas, including the Type 1 DNA polymerases from Escherichia coli and Thermus aquaticus, the mouse adipocyte lipid binding protein, and the classic allosteric enzyme aspartate transcarbamylase.

The Type 1 DNA polymerases from E. coli and T. aquaticus are a homologous mesophilic-thermophilic pair of proteins. Their molecular structures and basic catalytic functions are highly homologous, yet the T. aquaticus enzyme works near the boiling point of water, while the E. coli enzyme is irreversibly destroyed by exposure to 50oC. We directly and comparatively examine the DNA binding, protein folding, and global structural characteristics of these two species of DNA polymerases with the goal of delineating the exact differences and similarities between the two proteins in order to understand what features are necessary to achieve high temperature stability and activity for a DNA polymerase. We are in the midst of an extensive comparative characterization of the DNA binding properties and thermodynamic stabilities of the wildtype polymerases along with their “Klenow” and “Klentaq” large fragment domains. These studies include characterizations of DNA binding using fluorescence anisotropy and titration calorimetry, characterizations of stability using thermal and chemical denaturation methods, and characterization of structural and conformational changes using small angle X-ray scattering, analytical ultracentrifugation, and electrophoretic methods. We have just initiated site-directed mutagenesis and directed evolution studies aimed at elucidating the detailed structural features differentiating the two species of polymerase.

Mammalian adipocyte lipid binding protein (ALBP) is found in high concentrations in adipose cells, and has been strongly implicated in the development of Type 2 diabetes, obesity, and atherosclerosis. Our laboratory is studying the stability and lipid binding properties of ALBP, with emphasis on the control of these processes by electrostatics and environmental (solution) conditions. We have recently identified significant salt based regulatory effects on both the lipid binding and the stability of ALBP, and have begun characterizing the thermodynamic linkages among these processes (lipid binding, stability, and salt). We have also constructed site directed mutants of the protein and begun mapping the surface residues responsible for the regulation of the protein by ions.

Our laboratory is also characterizing the association and dissociation kinetics of both the polymerase-DNA and ALBP-lipid systems, in order to more precisely define the origins of solvent control in these systems. Protein-ligand equilibria and kinetics have long been known to be effected by nearly every aspect of their environment, including pH, salt, osmotic pressure, temperature, et cetera. As part of one ongoing project, our mapping of the effects of different environmental variables will soon be extended to examining the effects of gravity on the kinetics and equilibria of these reactions

E. coli aspartate transcarbamylase (ATCase) is one of the most extensively studied enzymes in biochemistry. It has served, and continues to serve in our laboratory as a benchmark for different studies, particularly our analytical ultracentrifugation and small angle X-ray scattering structural studies. We are, however, also investigating various hypotheses for explaining the mechanism of substrate inhibition in ATCase, and the mechanism of transmission of heterotropic allosteric regulatory signals within the enzyme.

Selected Publications

Datta, K, and LiCata, VJ, 2003, Salt dependence of DNA binding by Thermus aquaticus and Escherichia coli DNA polymerases, J. Biol. Chem. 278: 5694-5701.

Joubert, AM, Byrd, AS, and LiCata, VJ, 2003, Global conformations, hydrodynamics, and X-ray scattering properties of Taq and Escherichia coli DNA polymerases in solution, J. Biol. Chem. 278: 25341-25347.

Karantzeni, I., Ruiz, C.R., Liu, C.-C., and LiCata, V.J., 2003, Comparative thermal denaturation of Thermus aquaticus and Escherichia coli Pol 1 Type DNA polymerases, Biochem. J. 374, 785-792.

Schoeffler, A.J., Ruiz, C.R., Joubert, A.M., Yang, X., and LiCata, V.J., 2003, Salt modulates the stability and lipid binding affinity of the adipocyte lipid binding protein, J. Biol. Chem. 278, 33268-33275.



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