PF3D7_1448700

HSP20 (PF3D7_1448700) is a small heat shock protein required for the gliding motility and host migration of Plasmodium sporozoites (PMID:22139844). Genetic ablation of HSP20 in P. berghei sporozoites disrupts substrate adhesion and produces aberrant gliding speed and directionality in vitro, identifying HSP20 as a positive regulator of actin-based cell traction (PMID:22139844), and in vivo this defect impairs skin-to-liver migration and thereby the transmission-relevant steps of infection (PMID:22139844). Mechanistically, loss of HSP20 abrogates the polarized apical distribution of the acto-myosin motor component MTIP during gliding, indicating that HSP20 is needed for correct spatial organization of the motor complex during locomotion (PMID:31874192). Beyond these motility and MTIP-organization phenotypes established in P. berghei, no biochemical chaperone activity, direct binding partner, or substrate has been characterized for HSP20 in the available corpus.

1. 2011 High

   Whether this small heat shock protein contributes to parasite motility was unknown; knockout established that HSP20 is required for normal substrate adhesion and for the speed and directionality of sporozoite gliding.

   Evidence gene knockout with in vitro gliding motility and adhesion assays in P. berghei sporozoites

   PMID:22139844

   Open questions at the time

   • does not identify the molecular partners or substrates of HSP20
   • does not establish whether the defect reflects chaperone activity or a structural role
   • no biochemical demonstration of small heat shock protein function
2. 2011 High

   It was unclear whether the in vitro motility defect had consequences for infection; the knockout showed impaired sporozoite skin-to-liver migration, linking HSP20-dependent motility to natural transmission.

   Evidence gene knockout with in vivo host migration assays in P. berghei

   PMID:22139844

   Open questions at the time

   • does not resolve the molecular step at which migration fails
   • does not quantify contribution to overall infectivity beyond migration
3. 2019 Medium

   The mechanistic basis of the motility defect was unknown; comparison of MTIP localization in null versus wild-type sporozoites showed HSP20 is required for the polarized apical distribution of the acto-myosin motor component.

   Evidence immunofluorescence/microscopy of MTIP in HSP20 knockout versus wild-type P. berghei sporozoites

   PMID:31874192

   Open questions at the time

   • single lab, single method (localization only), no reciprocal or biochemical validation
   • does not show direct interaction between HSP20 and MTIP or motor components
   • does not establish whether HSP20 acts as a chaperone for motor assembly

• Whether HSP20 possesses chaperone activity and which client proteins or motor complex components it directly binds remains unresolved.
• no direct binding partner or substrate identified
• no structural or biochemical characterization of chaperone function
• no data in P. falciparum despite the PF3D7 identifier; all phenotypes derive from P. berghei