title: Identification of novel proteins in isolated polyphosphate vacuoles in the primitive red alga Cyanidioschyzon merolae.
abstract: Plant vacuoles are organelles bound by a single membrane, and involved in various functions such as intracellular digestion, metabolite storage, and secretion. To understand their evolution and fundamental mechanisms, characterization of vacuoles in primitive plants would be invaluable. Algal cells often contain polyphosphate-rich compartments, which are thought to be the counterparts of seed plant vacuoles. Here, we developed a method for isolating these vacuoles from Cyanidioschyzon merolae, and identified their proteins by MALDI TOF-MS. The vacuoles were of unexpectedly high density, and were highly enriched at the boundary between 62 and 80% w/v iodixanol by density-gradient ultracentrifugation. The vacuole-containing fraction was subjected to SDS-PAGE, and a total of 46 proteins were identified, including six lytic enzymes, 13 transporters, six proteins for membrane fusion or vesicle trafficking, five non-lytic enzymes, 13 proteins of unknown function, and three miscellaneous proteins. Fourteen proteins were homologous to known vacuolar or lysosomal proteins from seed plants, yeasts or mammals, suggesting functional and evolutionary relationships between C. merolae vacuoles and these compartments. The vacuolar localization of four novel proteins, namely CMP249C (metallopeptidase), CMJ260C (prenylated Rab receptor), CMS401C (ABC transporter) and CMT369C (o-methyltransferase), was confirmed by labeling with specific antibodies or transient expression of hemagglutinin-tagged proteins. The results presented here provide insights into the proteome of C. merolae vacuoles and shed light on their functions, as well as indicating new features.
authors.affiliation: Research Information Center for Extremophiles, Rikkyo (St Paul's) University, Nishi-Ikebukuro, Tokyo 171-8501, Japan. z20022379@rikkyo.ne.jp
authors.forename: Fumi
authors.initials: F
authors.lastname: Yagisawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Nishida
authors.forename: Masaki
authors.initials: M
authors.lastname: Yoshida
authors.forename: Mio
authors.initials: M
authors.lastname: Ohnuma
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimada
authors.forename: Takayuki
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Yamato
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Osami
authors.initials: O
authors.lastname: Misumi
authors.forename: Haruko
authors.initials: H
authors.lastname: Kuroiwa
authors.forename: Tsuneyoshi
authors.initials: T
authors.lastname: Kuroiwa
mesh_terms: D020418:Algal Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D016678:Genome; D011122:Polyphosphates / Q000378:metabolism; D020543:Proteome; D000461:Rhodophyta / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014617:Vacuoles / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D020418:Algal Proteins; D011122:Polyphosphates; D020543:Proteome