title: Giardia lamblia: identification and characterization of Rab and GDI proteins in a genome survey of the ER to Golgi endomembrane system.
abstract: To investigate the complexity of the endomembrane transport system in the early diverging eukaryote, Giardia lamblia, we characterized homologues of the GTP-binding proteins, Rab1 and Rab2, involved in regulating vesicular trafficking between the endoplasmic reticulum and Golgi in higher eukaryotes, and GDI, which plays a key role in the cycling of Rab proteins. G. lamblia Rab1, 2.1, and GDI sequences largely resemble yeast and mammalian homologues, are transcribed as 0.66-, 0.62-, and 1.4-kb messages, respectively, and are expressed during growth and encystation. Western analyses detected an abundant Rab/GDI complex at approximately 80 kDa, and free GDI (60 kDa) in both trophozoites and encysting cells. Immunoelectron microscopy with antibody to Rab1 localized Rab with ER, encystation secretory vesicles, and lysosome-like peripheral vesicles. GDI associated with these structures, and with small vesicles found throughout the cytoplasm, consistent with GDI's key role in Rab cycling between organelles within the cell.
authors.affiliation: Division of Infectious Diseases, Department of Pathology, University of California, San Diego, CA 92103-8416, USA.
authors.forename: T Dianne
authors.initials: TD
authors.lastname: Langford
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Silberman
authors.forename: Malin E-L
authors.initials: ME
authors.lastname: Weiland
authors.forename: Staffan G
authors.initials: SG
authors.lastname: Svärd
authors.forename: J Michael
authors.initials: JM
authors.lastname: McCaffery
authors.forename: Mitchell L
authors.initials: ML
authors.lastname: Sogin
authors.forename: Frances D
authors.initials: FD
authors.lastname: Gillin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D004721:Endoplasmic Reticulum / Q000502:physiology*; D005786:Gene Expression Regulation; D018503:Genome, Protozoan; D016829:Giardia lamblia / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000502:physiology*; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D007425:Intracellular Membranes / Q000502:physiology; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D014158:Transcription, Genetic
chemical_list: C086796:GDP dissociation inhibitor 1; C098085:Gdi2 protein, mouse; D020730:Guanine Nucleotide Dissociation Inhibitors