AMA2

AMA2 is a paralog of the invasion adhesin AMA1 in Toxoplasma gondii that functions within the moving junction (MJ) machinery to support host cell invasion (PMID:24934579, PMID:36693095). When AMA1 is genetically disrupted in tachyzoites, AMA2 is upregulated together with RON2 homologues and cooperates with them to sustain residual parasite internalization, revealing functional plasticity and redundancy among AMA–RON invasion pairs (PMID:24934579). AMA2 additionally serves a stage-specific role: in bradyzoites, the MJ is built from AMA2 and AMA4 rather than the tachyzoite adhesin AMA1, indicating that AMA2 is deployed as a dedicated MJ component for bradyzoite-stage invasion (PMID:36693095). Beyond its participation in MJ assembly and its cooperation with RON2 homologues, no further mechanistic detail on AMA2 — including direct binding partners, structural basis, or regulation — has been characterized in the available corpus.

1. 2014 High

   Whether Toxoplasma invasion depends strictly on AMA1 or can proceed through alternative adhesins was unknown; disrupting AMA1 revealed a compensatory system in which AMA2 is upregulated and cooperates with RON2 homologues to preserve residual invasion.

   Evidence Reverse genetics disruption of AMA1 with homologue upregulation analysis and functional invasion assays in T. gondii

   PMID:24934579

   Open questions at the time

   • Direct binding of AMA2 to specific RON2 homologues not biochemically defined
   • Contribution of AMA2 to invasion in the presence of intact AMA1 not established
   • Structural basis of AMA2 function within the MJ not determined
2. 2023 Medium

   Whether the same MJ adhesins operate across parasite life stages was unresolved; characterization of the bradyzoite MJ showed that AMA2 and AMA4 replace tachyzoite AMA1, establishing AMA2 as a stage-specific invasion component.

   Evidence Molecular and biochemical characterization of bradyzoite MJ composition with stage-specific invasion assays; loss-of-function analysis focused on AMA4 in T. gondii

   PMID:36693095

   Open questions at the time

   • AMA2 role inferred from MJ composition data rather than direct AMA2 loss-of-function
   • RON partner of AMA2 in bradyzoites not defined
   • Mechanism regulating stage-specific AMA2 deployment unknown

• Whether AMA2 has a distinct, non-redundant function and which specific RON partners and structural interfaces mediate its role in the moving junction remain unresolved.
• No direct AMA2 loss-of-function phenotype reported
• No structural model of AMA2–RON interactions
• Transcriptional/regulatory control of AMA2 expression uncharacterized