Biochemistry and Molecular Biology (BIO)
Uniformed Services University of the Health Sciences
Department of Biochemistry and Molecular Biology
4301 Jones Bridge Road, C1094
Bethesda, Maryland 20814-4799
Fax: (301) 295-3512
Lab: (301) 295-3462
Professor & Chair
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 a-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.
- Sphingolipids in the root play an important role in regulating the leaf ionome in Arabidopsis thaliana. Chao DY, Gable K, Chen M, Baxter I, Dietrich CR, Cahoon EB, Guerinot ML, Lahner B, Lü S, Markham JE, Morrissey J, Han G, Gupta SD, Harmon JM, Jaworski JG, Dunn TM, Salt DE. Plant Cell. 2011 Mar;23(3):1061-81.
- A disease-causing mutation in the active site of serine palmitoyltransferase causes catalytic promiscuity.Gable K, Gupta SD, Han G, Niranjanakumari S, Harmon JM, Dunn TM. J Biol Chem. 2010 Jul 23;285(30):22846-52.
- Overexpression of the wild-type SPT1 subunit lowers desoxysphingolipid levels and rescues the phenotype of HSAN1. Eichler FS, Hornemann T, McCampbell A, Kuljis D, Penno A, Vardeh D, Tamrazian E, Garofalo K, Lee HJ, Kini L, Selig M, Frosch M, Gable K, von Eckardstein A, Woolf CJ, Guan G, Harmon JM, Dunn TM, Brown RH Jr. J Neurosci. 2009 Nov 18;29(46):14646-51.
- Identification of small subunits of mammalian serine palmitoyltransferase that confer distinct acyl-CoA substrate specificities. Han G, Gupta SD, Gable K, Niranjanakumari S, Moitra P, Eichler F, Brown RH Jr, Harmon JM, Dunn TM. Proc Natl Acad Sci U S A. 2009 May 19;106(20):8186-91.
- Tsc10p and FVT1: topologically distinct short-chain reductases required for long-chain base synthesis in yeast and mammals. Gupta SD, Gable K, Han G, Borovitskaya A, Selby L, Dunn TM, Harmon JM. J Lipid Res. 2009 Aug;50(8):1630-40.
- Arabidopsis mutants lacking long chain base phosphate lyase are fumonisin-sensitive and accumulate trihydroxy-18:1 long chain base phosphate. Tsegaye Y, Richardson CG, Bravo JE, Mulcahy BJ, Lynch DV, Markham JE, Jaworski JG, Chen M, Cahoon EB, Dunn TM. J Biol Chem. 2007 Sep 21;282(38):28195-206.