Department of Biochemistry
and Molecular Biology

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• 2010 Arabidopsis Sphingolipid Project

Research interests

The research interests in my lab are focused on identifying and characterizing the enzymes responsible for sphingolipid synthesis, on determining how sphingolipid synthesis is regulated, and on elucidating the physiological functions of these important lipids.A combined genetic and biochemical approach using the model eukaryote, Saccharomycescerevisiae is being used.The sphingolipids in Saccharomyces cerevisiae contain a mannosyldiinositolphosphoryl head group attached to a ceramide.The ceramide is comprised of an α-hydroxy-C26-fatty acid and phytosphingosine.We discovered that deletion of either the CSG1 or CSG2 gene results in inability to efficiently mannosylate inositolphosphorylceramide and consequently in the overaccumulation of inositolphosphorylceramide (1-3).Although these mutants grow normally under most conditions, they are exquisitely sensitive to Ca2+, and the sensitivity to Ca2+ is correlated with the overaccumulation of inositolphosphorylceramide due to the block in mannosylation.Based on this observation, we devised screens for second-site suppressor mutants that reverse the Ca2+ sensitivity of the csg2 mutant.Because many of the suppressor mutations reduce the synthesis of inositolphosphorylceramide, these genetic screens have been extremely powerful at identifying sphingolipid biosynthetic genes.Initially we screened for suppressors at 37oC and generated the SCS (Suppressor of Ca Sensitivity) collection (3-6).However, as our understanding of the suppressor mutants evolved, we realized there would be advantages to screening for suppressors at 26oC and doing secondary screens to identify the subset of suppressors that had an associated temperature sensitive lethal phenotype.Thus, we did a second suppressor mutant screen to identify the TSC (Ts Suppressors of Ca Sensitivity) collection (5, 7, 8).Through the characterization of the TSC and SCS genes, we have identified and characterized many of the genes encoding proteins required for very long chain fatty acid (VLCFA) and long chain base (LCB) synthesis.

The long-term goal is to identify and characterize the proteins required for fatty acid elongation, to determine how the proteins are organized, to establish how synthesis of the VLCFAs is regulated, and to determine the essential functions of the VLCFAs.The immediate goal is to determine the specific functions of Elo2p, Elo3p, and Tsc13p, to identify the other elongating proteins, and to determine how the elongating proteins are organized.The elongase mutants provide the basis for biochemical and genetic studies that will identify other proteins required for VLCFA synthesis.The characterization of the proteins required for VLCFA synthesis is expected to advance the understanding of this important pathway, not only in yeast, but also in all eukaryotic cells.We have recently determined that TSC13 encodes the enoyl reductase (9), and that the YBR159 gene encodes the major 3-ketoreductase of the elongase system (10, 11).We are collaborating with Johnathan Napier in these studies.

Selected publications

• "A Saccharomyces cerevisiae gene required for heterologous fatty acid elongase activity encodes a microsomal beta-keto-reductase." Beaudoin, F., K. Gable, O. Sayanova, T. Dunn, and J.A. Napier.( 2002). J Biol Chem. 277:11481-8.
• "Mutations in the Lcb2p subunit of serine palmitoyltransferase eliminate the requirement for the TSC3 gene in Saccharomyces cerevisiae." Monaghan, E., K. Gable, and T. Dunn. (2002) Yeast. 19:659-70.
• "Mutations in the Yeast LCB1 and LCB2 Genes, Including Those Corresponding to the Hereditary Sensory Neuropathy Type I Mutations, Dominantly Inactivate Serine Palmitoyltransferase." Gable, K., Han, G.,Monaghan E.,Bacikova, D,Natarajan, M.,Williams, R. & Dunn, T.M. (2002). J. Biol. Chem. 277:10194-10200.