NSF

In Toxoplasma gondii, NSF is a component of the vesicle-fusion machinery that drives constitutive, calcium-independent dense granule exocytosis (PMID:9891012). In streptolysin O-permeabilized parasites, recombinant hamster NSF together with bovine alpha-SNAP augmented dense granule release, while N-ethylmaleimide (an NSF inhibitor) and recombinant Rab-GDI blocked it, placing NSF, SNAP, SNAREs, and Rab GTPases in a common secretory pathway (PMID:9891012). Secretion was stimulated by GTPgammaS but not cAMP and required ATP, positioning Rab GTPase activity upstream of NSF/SNAP-mediated fusion (PMID:9891012). Beyond this single reconstitution study, no further mechanistic detail on Toxoplasma NSF has been characterized in the available corpus.

1. 1999 High

   It was unknown whether T. gondii dense granule secretion used the conserved NSF/SNAP/SNARE/Rab fusion machinery and how it was regulated; reconstitution in permeabilized parasites established this machinery drives constitutive, calcium-independent release with Rab GTPase activity upstream of fusion.

   Evidence Streptolysin O-permeabilized parasite secretion assays with recombinant mammalian NSF, alpha-SNAP and Rab-GDI, N-ethylmaleimide inhibition, beta-lactamase reporter, and GTPgammaS/cAMP stimulation

   PMID:9891012

   Open questions at the time

   • The endogenous T. gondii NSF protein was not cloned or characterized; recombinant mammalian orthologs were used as surrogates
   • The specific SNARE substrates and Rab GTPase(s) acting in this pathway were not identified
   • No structural or biochemical characterization of the parasite NSF itself

• The identity and biochemistry of the endogenous Toxoplasma NSF, its cognate SNAREs, and the Rab GTPase(s) coordinating dense granule fusion remain uncharacterized.
• No characterization of endogenous parasite NSF protein
• No identified SNARE or Rab partners specific to dense granule exocytosis