Dr. Edgar Kooijman | Kent State University

"Biophysical characterization of Protein-Lipid interactions"

Research in the Kooijman laboratory is currently divided into two distinct directions.

One project involves the physicochemical characterization of signaling lipids containing phosphomonoester moieties (in their headgroup). Examples of such lipids are phosphatidic acid, ceramide-1-phosphate, their derivatives and the polyphosphoinositides. We are specialized in determining the ionization properties of these lipids in complex lipid mixtures. As the pKa of these lipids falls in the physiological pH range and their charge is sensitively influenced by their environment, gaining knowledge of exactly what influences the exact charge is crucial. This was recently highlighted by a seminal work by Loewen et al, [1] who showed that transcriptional regulation of lipid synthesis is closely tied to the metabolic state of a yeast cell via the pH sensitive binding of a transcriptional repressor on the ER. The binding partner of this repressor turns out to be a lipid, namely phosphatidic acid. Without our work on the ionization properties of PA such an explanation would have been impossible to derive at [2,3]. Current projects in the lab revolve around the lipid DGPP which is mainly found in plants, but also yeast, and a continuation of the work on PI(4,5)P2. The main technique employed is solid state NMR coupled with a host of wet lipid chemistry work.

Another project is centered on the role of protein-lipid interactions in the formation of neutral lipid particles crucial to fat transport and storage. Specifically the topic of lipid storage in neutral lipid droplets is of high current interest. A subset of the proteins involved in the process of droplet formation and regulation is able to cycle on and off the particle and contain an amphipatic alpha-helix bundle domain that is able to reversibly unfold (it's ternary structure) and cover portions of the droplet surface. The exact interactions responsible for this binding and its reversible nature are currently unknown. We use a model amphipatic alpha-helix protein, apoLpIII from Locusta Migratoria to investigate protein-lipid interactions using both Langmuir monolayer and Surface Plasmon Resonance techniques. In the case of the monolayer experiments we perform monolayer insertion experiments and occasional travel to the Synchrotron in Chicago for structural studies of this protein at air-water and water-lipid-air interfaces. We are currently also synthesizing proteins from the PERILIPIN family of lipid droplet proteins to be used in these studies.

REU students have, in the past, worked on each of these two projects. At least one publication is expected from the work carried out this past summer on the lipid DGPP. You will be expected to work together with other students and postdoc in the lab, and if possible should see your work published in future publications.

  1. Young, B. P., Shin, J. J. H., Orij, R., Chao, J. T., Li, S. C., Guan, X. L., Khong, A., Jan, E., Wenk, M. R., Prinz, W. A., Smits, G. J., Loewen, C. J. R. (2010) Phosphatidic acid is a pH biosensor that links membrane biogenesis to metabolism. Science 329: 1085-1088
  2. Kooijman, E. E., Carter, K. M., van Laar, E. G., Chupin, V., Burger, K. N. and de Kruijff, B. (2005) What makes the bioactive lipids phosphatidic acid and lysophosphatidic acid so special? Biochemistry. 44, 17007-17015
  3. Kooijman, E. E., Tieleman, D. P., Testerink, C., Munnik, T., Rijkers, D. T., Burger, K. N. and de Kruijff, B. (2007) An electrostatic/hydrogen bond switch as the basis for the specific interaction of phosphatidic acid with proteins. J Biol Chem. 282, 11356-11364