Syntaxin 7, syntaxin 8, Vti1 and VAMP7 (vesicle-associated membrane protein 7) form an active SNARE complex for early macropinocytic compartment fusion in Dictyostelium discoideum

Biochem J. 2002 Nov 15;368(Pt 1):29-39. doi: 10.1042/BJ20020845.

Abstract

The macropinocytic pathway in Dictyostelium discoideum is organized linearly. After actin-driven internalization, fluid material passes sequentially from endosomes to lysosomes, where molecules are degraded and absorbed. Residual material is exocytosed via post-lysosomal compartments. Syntaxin 7 is a SNARE (soluble N -ethylmaleimide-sensitive fusion protein attachment protein receptor) protein that is present and active in D. discoideum endosomes [Bogdanovic, Bruckert, Morio and Satre (2000) J. Biol. Chem. 275, 36691-36697]. Here we report the identification of its main SNARE partners by co-immunoprecipitation and MS peptide sequencing. The syntaxin 7 complex contains two co-t-SNAREs [Vti1 (Vps10p tail interactor 1) and syntaxin 8] and a v-SNARE [VAMP7 (vesicle-associated membrane protein 7)] (where t-SNAREs are SNAREs of the target compartment and v-SNAREs are SNAREs present in donor vesicles). In endosomes and in vitro, syntaxin 7, Vti1 and syntaxin 8 form a complex that is able to bind VAMP7. Antibodies to syntaxin 8 and a soluble recombinant VAMP7 fragment both inhibit in vitro reconstituted D. discoideum endosome fusion. The lysosomal content of syntaxin 7, Vti1, syntaxin 8 and VAMP7 is low compared with that in endosomes, implying a highly active recycling or retention mechanism. A likely model is that VAMP7 is a v-SNARE present on vesicles carrying lysosomal enzymes, and that the syntaxin 7-Vti1-syntaxin 8 t-SNARE complex is associated with incoming endocytic material.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Carrier Proteins / metabolism*
  • Dictyostelium / metabolism*
  • Endosomes / metabolism
  • Humans
  • Membrane Fusion
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Pinocytosis
  • Protozoan Proteins / metabolism*
  • Qa-SNARE Proteins
  • Qb-SNARE Proteins
  • R-SNARE Proteins
  • SNARE Proteins
  • Vesicular Transport Proteins*

Substances

  • Carrier Proteins
  • Membrane Proteins
  • Protozoan Proteins
  • Qa-SNARE Proteins
  • Qb-SNARE Proteins
  • R-SNARE Proteins
  • SNARE Proteins
  • VAMP7 protein, human
  • VTI1A protein, human
  • Vesicular Transport Proteins