Cloning and Sequencing of a Protein Involved in Phagosomal Membrane Fusion inParamecium
| Autor: | Marilynn S. Aihara, Kiyoshi Yamauchi, Masaki Ishida, Agnes K. Fok, Richard D. Allen |
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| Rok vydání: | 1999 |
| Předmět: |
Signal peptide
DNA Complementary Paramecium Molecular Sequence Data Restriction Mapping Antigens Protozoan Vacuole Biology Membrane Fusion Article Phagosomes Organelle Animals Amino Acid Sequence Cloning Molecular Codon Molecular Biology Base Sequence Sequence Homology Amino Acid Vesicle Antibodies Monoclonal Lipid bilayer fusion Intracellular Membranes Cell Biology Cell biology Molecular Weight Transmembrane domain Membrane Membrane protein Antigens Surface Vacuoles Sequence Alignment |
| Zdroj: | Molecular Biology of the Cell. 10:1031-1041 |
| ISSN: | 1939-4586 1059-1524 |
| DOI: | 10.1091/mbc.10.4.1031 |
| Popis: | An mAb was raised to the C5 phagosomal antigen in Paramecium multimicronucleatum. To determine its function, the cDNA and genomic DNA encoding C5 were cloned. This antigen consisted of 315 amino acid residues with a predicted molecular weight of 36,594, a value similar to that determined by SDS-PAGE. Sequence comparisons uncovered a low but significant homology with aSchizosaccharomyces pombe protein and the C-terminal half of the β-fructofuranosidase protein of Zymomonas mobilis. Lacking an obvious transmembrane domain or a possible signal sequence at the N terminus, C5 was predicted to be a soluble protein, whereas immunofluorescence data showed that it was present on the membranes of vesicles and digestive vacuoles (DVs). In cells that were minimally permeabilized but with intact DVs, C5 was found to be located on the cytosolic surface of the DV membranes. Immunoblotting of proteins from the purified and KCl-washed DVs showed that C5 was tightly bound to the DV membranes. Cryoelectron microscopy also confirmed that C5 was on the cytosolic surface of the discoidal vesicles, acidosomes, and lysosomes, organelles known to fuse with the membranes of the cytopharynx, the DVs of stages I (DV-I) and II (DV-II), respectively. Although C5 was concentrated more on the mature than on the young DV membranes, the striking observation was that the cytopharyngeal membrane that is derived from the discoidal vesicles was almost devoid of C5. Approximately 80% of the C5 was lost from the discoidal vesicle-derived membrane after this membrane fused with the cytopharyngeal membrane. Microinjection of the mAb to C5 greatly inhibited the fusion of the discoidal vesicles with the cytopharyngeal membrane and thus the incorporation of the discoidal vesicle membranes into the DV membranes. Taken together, these results suggest that C5 is a membrane protein that is involved in binding and/or fusion of the discoidal vesicles with the cytopharyngeal membrane that leads to DV formation. |
| Databáze: | OpenAIRE |
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