title: Identification of a Major Lipid Droplet Protein in a Marine Diatom Phaeodactylum tricornutum.
abstract: Various kinds of organisms, including microalgae, accumulate neutral lipids in distinct intracellular compartments called lipid droplets. Generally, lipid droplets are generated from the endoplasmic reticulum, and particular proteins localize on their surface. Some of these proteins function as structural proteins to prevent fusion between the lipid droplets, and the others could have an enzymatic role or might be involved in intracellular membrane trafficking. However, information about lipid droplet proteins in microalgae is scarce as compared with that in animals and land plants. We focused on the oil-producing, marine, pennate diatom Phaeodactylum tricornutum that forms lipid droplets during nitrogen deprivation and we investigated the proteins located on the lipid droplets. After 6 d of cultivation in a nitrate-deficient medium, the mature lipid droplets were isolated by sucrose density gradient centrifugation. Proteomic analyses revealed five proteins, with Stramenopile-type lipid droplet protein (StLDP) being the most abundant protein in the lipid droplet fraction. Although the primary sequence of StLDP did not have homology to any known lipid droplet proteins, StLDP had a central hydrophobic domain. This structural feature is also detected in oleosin of land plants and in lipid droplet surface protein (LDSP) of Nannochloropsis species. As a proline knot motif of oleosin, conservative proline residues existed in the hydrophobic domain. StLDP was up-regulated during nitrate deprivation, and fluctuations of StLDP expression levels corresponded to the size of the lipid droplets.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572 Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Yoneda
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572 Japan yoshida.masaki.gb@u.tsukuba.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Yoshida
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572 Japan.
authors.forename: Iwane
authors.initials: I
authors.lastname: Suzuki
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572 Japan.
authors.forename: Makoto M
authors.initials: MM
authors.lastname: Watanabe
mesh_terms: D000595:Amino Acid Sequence; D059001:Aquatic Organisms / Q000378:metabolism*; D017377:Diatoms / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D066292:Lipid Droplets / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D008565:Membrane Proteins; D012333:RNA, Messenger
keywords: Diatom; Lipid droplet protein; Nitrogen deprivation; Oleosin; Phaeodactylum tricornutum; Proteomic analysis