DRPB

DrpB is an alveolate-specific dynamin-related protein that drives biogenesis of the regulated secretory organelles in Toxoplasma gondii (PMID:19217293). It localizes to a cytoplasmic region close to the Golgi, dispersing during replication and reforming after daughter-cell assembly, consistent with a vesicle-generating mechanoenzyme acting during the secretory-organelle assembly phase of the cell cycle (PMID:19217293). Conditional ablation of DrpB yields mature daughter parasites completely devoid of micronemes and rhoptries, with invasion-related secretory cargo mistargeted to the constitutive secretory pathway, placing DrpB at the step that segregates regulated from constitutive secretion (PMID:19217293). DrpB operates specifically in the exocytic arm of a trafficking route shared with host-protein endocytosis through early/late endosome-like compartments; it is dispensable for endocytosis of host-derived proteins (PMID:29437275). Beyond these findings, the enzymatic and structural details of DrpB have not been characterized in the available corpus.

1. 2009 High

   Establishing whether a dedicated machinery generates the vesicles that build the invasion organelles, this work identified DrpB as an alveolate-specific dynamin-related protein essential for microneme and rhoptry biogenesis.

   Evidence Conditional ablation, fluorescence localization, and secretory-organelle phenotyping in T. gondii

   PMID:19217293

   Open questions at the time

   • No demonstration of the biochemical mechanoenzyme activity (GTP hydrolysis or membrane scission)
   • Direct binding partners and recruitment mechanism to the Golgi-proximal site unresolved
   • No structural model of DrpB
2. 2018 Medium

   To determine whether DrpB acts broadly across membrane trafficking or specifically in exocytosis, a dominant-negative mutant showed DrpB is dispensable for host-protein endocytosis and functions in the exocytic arm of a route shared with endocytosis through endosome-like compartments.

   Evidence Conditional dominant-negative expression with colocalization of host-derived proteins and immature organelle markers plus live-cell trafficking in T. gondii

   PMID:29437275

   Open questions at the time

   • Dominant-negative approach does not pinpoint the direct molecular step DrpB catalyzes
   • Molecular components of the shared endosome-like compartment engaged by DrpB not defined
   • Whether DrpB directly deforms/scissions vesicles at these compartments not shown

• The direct biochemical activity of DrpB, its recruitment machinery, and the identity of its membrane and protein partners remain unresolved.
• No demonstrated GTPase or membrane-scission activity in the corpus
• No identified interacting proteins or adaptors
• No structural characterization