A syntaxin 7 homologue is present in Dictyostelium discoideum endosomes and controls their homotypic fusion.
Endo-phagocytic activity is prominent in Dictyostelium discoideum and makes it a good model organism to study the molecular organization of membrane traffic in this pathway. We have identified a syntaxin 7 homologue (26% identity and 54% similarity to human syntaxin 7) in Dictyostelium cDNA and genomic data banks. In addition to the Habc and H3 helices and the C-terminal transmembrane domain characteristic of syntaxins, this protein contains a repetitive N-terminal extension of 68 amino acids. We first showed that Dictyostelium syntaxin 7 was able to form a complex with N-ethylmaleimide-sensitive fusion protein and alpha- and gamma-soluble N-ethylmaleimide-sensitive fusion protein attachment protein. Its intracellular localization was then studied by cell fractionation techniques and magnetic purification of the endocytic compartments. Most of D. discoideum syntaxin 7 is contained in endosomes. Finally, an in vitro endosome homotypic fusion assay (Laurent, O., Bruckert, F., Adessi, C., and Satre, M. (1998) J. Biol. Chem. 273, 793-799) was used to study a possible role for syntaxin 7 in this process. Purified anti-syntaxin 7 antibodies and a recombinant soluble fragment of syntaxin 7 both strongly inhibited fusion activity, indicating that this protein was necessary for endosome-endosome fusion. These results demonstrate the importance of this syntaxin 7 homologue in the early phases of Dictyostelium endo-phagocytic pathway.
Bogdanovic
A
A
From the Laboratoire de Biochimie et Biophysique des Systèmes Intégrés, Département de Biologie Moléculaire et Structurale, 38054 Grenoble Cedex 9, France.
Bruckert
F
F
Morio
T
T
Satre
M
M
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002499:Centrifugation, Density Gradient; D004023:Dictyostelium / Q000737:chemistry*; D011992:Endosomes / Q000737:chemistry*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D050765:Qa-SNARE Proteins; D017386:Sequence Homology, Amino Acid
D008565:Membrane Proteins; D050765:Qa-SNARE Proteins