title: A six-membrane-spanning topology for yeast and Arabidopsis Tsc13p, the enoyl reductases of the microsomal fatty acid elongating system.
abstract: The very long chain fatty acids are crucial building blocks of essential lipids, most notably the sphingolipids. These elongated fatty acids are synthesized by a system of enzymes that are organized in a complex within the endoplasmic reticulum membrane. Although several of the components of the elongase complex have recently been identified, little is known about how these proteins are organized within the membrane or about how they interact with one another during fatty acid elongation. In this study the topology of Tsc13p, the enoyl reductase of the elongase system, was investigated. The N and C termini of Tsc13p reside in the cytoplasm, and six putative membrane-spanning domains were identified by insertion of glycosylation and factor Xa cleavage sites at various positions. The N-terminal domain including the first membrane-spanning segment contains sufficient information for targeting to the endoplasmic reticulum membrane. Studies of the Arabidopsis Tsc13p protein revealed a similar topology. Highly conserved domains of the Tsc13p proteins that are likely to be important for enzymatic activity lie on the cytosolic face of the endoplasmic reticulum, possibly partially embedded within the membrane.
authors.affiliation: Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20184, USA.
authors.forename: Shilpi
authors.initials: S
authors.lastname: Paul
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gable
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Dunn
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000737:chemistry* / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D005227:Fatty Acids; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D010088:Oxidoreductases; D044943:Fatty Acid Desaturases; C522632:Tsc13 protein, Arabidopsis; D044925:Oxidoreductases Acting on CH-CH Group Donors; C418219:TSC13 protein, S cerevisiae