title: Traffic of human α-mannosidase in plant cells suggests the presence of a new endoplasmic reticulum-to-vacuole pathway without involving the Golgi complex.
abstract: The transport of secretory proteins from the endoplasmic reticulum to the vacuole requires sorting signals as well as specific transport mechanisms. This work is focused on the transport in transgenic tobacco (Nicotiana tabacum) plants of a human α-mannosidase, MAN2B1, which is a lysosomal enzyme involved in the turnover of N-linked glycoproteins and can be used in enzyme replacement therapy. Although ubiquitously expressed, α-mannosidases are targeted to lysosomes or vacuoles through different mechanisms according to the organisms in which these proteins are produced. In tobacco cells, MAN2B1 reaches the vacuole even in the absence of mannose-6-phosphate receptors, which are responsible for its transport in animal cells. We report that MAN2B1 is targeted to the vacuole without passing through the Golgi complex. In addition, a vacuolar targeting signal that is recognized in plant cells is located in the MAN2B1 amino-terminal region. Indeed, when this amino-terminal domain is removed, the protein is retained in the endoplasmic reticulum. Moreover, when this domain is added to a plant-secreted protein, the resulting fusion protein is partially redirected to the vacuole. These results strongly suggest the existence in plants of a new type of vacuolar traffic that can be used by leaf cells to transport vacuolar proteins.
authors: Istituto di Genetica Vegetale, Consiglio Nazionale delle Ricerche, 06128 Perugia, Italy.
authors: Francesca
authors: F
authors: De Marchis
authors: Michele
authors: M
authors: Bellucci
authors: Andrea
authors: A
authors: Pompa
mesh_terms: D020126:Brefeldin A / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D059828:Plant Cells / Q000187:drug effects / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000378:metabolism; D017510:Protein Folding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D043323:alpha-Mannosidase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D011134:Polysaccharides; D020126:Brefeldin A; D043323:alpha-Mannosidase