PCR5

PCR5 (Pcr5) is a structural component of the preconoidal rings (PCRs) at the apical tip of Toxoplasma gondii, where it participates in an apical hub that gates parasite motility and invasion (PMID:36109645). It contains a B-box zinc-finger domain and assembles as a heterodimer with Pcr4, an interaction essential for formation of the preconoidal ring structure itself (PMID:36109645). The PCRs serve as a recruitment hub for glideosome components including Formin1, thereby coupling apical ring architecture to conoid extrusion and F-actin flux that drive motility and host-cell invasion (PMID:36109645). Beyond this PCR structural and glideosome-recruitment role established in T. gondii, no further biochemical or mechanistic detail for PCR5 has been characterized in the available corpus.

1. 2022 Medium

   Establishing where glideosome activity is organized at the parasite apex, the preconoidal rings were shown to serve as a hub for glideosome components, linking an apical ultrastructure to the motility machinery.

   Evidence Ultrastructure expansion microscopy localizing Formin1 and other glideosome components to the PCRs in Toxoplasma gondii

   PMID:36109645

   Open questions at the time

   • Does not define the direct binding interactions between PCR proteins and recruited glideosome factors
   • Molecular mechanism by which the PCR hub controls conoid extrusion is not resolved
2. 2022 Medium

   To define what builds the preconoidal ring, Pcr5 was identified as a B-box zinc-finger protein that heterodimerizes with Pcr4 and is essential for ring formation, establishing it as a required structural subunit rather than a peripheral component.

   Evidence U-ExM localization, essentiality/genetic perturbation, and protein interaction/complex assembly analysis in Toxoplasma gondii

   PMID:36109645

   Open questions at the time

   • No structural model of the Pcr4-Pcr5 heterodimer or its arrangement within the ring
   • Role of the B-box zinc-finger domain in dimerization or ring assembly not dissected
   • Whether Pcr5 directly contacts glideosome components is not established
3. 2022 Medium

   To place PCR5 in a biological pathway, the Pcr4/Pcr5 module was shown to be conserved across Apicomplexa and to gate motility and invasion through control of conoid extrusion and F-actin flux, defining the functional output of the apical hub.

   Evidence Comparative genomics with U-ExM and motility/invasion functional assays in Toxoplasma gondii

   PMID:36109645

   Open questions at the time

   • Mechanistic coupling between ring integrity and F-actin flux is not defined
   • Contribution of PCR5 in other apicomplexan species not experimentally tested

• How the Pcr4/Pcr5 heterodimer mechanically transmits signals or scaffolds glideosome components to control conoid extrusion and actin dynamics remains unresolved.
• No direct biochemical map of PCR5 partner contacts beyond the Pcr4 heterodimer
• No high-resolution structure of the assembled preconoidal ring