CERLI2

CERLI2 (PF3D7_0405200) is a rhoptry bulb protein essential for erythrocyte invasion during the blood stage of Plasmodium falciparum (PMID:35140336). It localises to the cytosolic face of the rhoptry bulb membrane in merozoites (PMID:35140336). Inducible knockdown inhibits blood-stage growth and causes a proportion of merozoites to fail to invade erythrocytes, alongside elongation of the rhoptry organelle and impaired rhoptry antigen processing, placing CERLI2 in rhoptry biogenesis and function during invasion (PMID:35140336). High-resolution ultrastructure expansion microscopy resolves the biogenesis defect to morphological alterations of the rhoptry necks, distinguishing CERLI2 from other rhoptry biogenesis factors (PMID:39292724). In P. berghei, the cerli2 locus is a direct transcriptional target of the AP2 factor PbSIP2 during schizogony (PMID:40117352). Beyond these findings, no molecular activity, direct protein partners, or structural mechanism for CERLI2 has been characterized in the available corpus.

1. 2020 Low

   Before direct functional work, it was unknown whether CERLI2 was a distinct player in invasion; bioinformatic comparison flagged it as structurally similar to PfCERLI1 with shared predicted epitopes, raising the question of functional redundancy and prior implication in merozoite invasion.

   Evidence Bioinformatic sequence/structure comparison in P. falciparum

   PMID:32179747

   Open questions at the time

   • Computational prediction only, no direct experiment on CERLI2 in this paper
   • Structural similarity does not establish shared or independent function
   • No localization or loss-of-function data
2. 2022 Medium

   To place CERLI2 in the invasion machinery, its subcellular position was resolved, establishing it as a peripheral rhoptry bulb protein facing the cytosol rather than a lumenal or secreted factor.

   Evidence Subcellular fractionation and fluorescence microscopy in P. falciparum merozoites

   PMID:35140336

   Open questions at the time

   • Membrane anchoring mechanism not defined
   • No direct binding partners at the rhoptry membrane identified
   • Single lab
3. 2022 High

   The question of whether CERLI2 is required for invasion was answered by conditional depletion, which arrested blood-stage growth and blocked a proportion of merozoites from invading erythrocytes, defining CERLI2 as essential.

   Evidence Inducible knockdown with growth and invasion assays in P. falciparum

   PMID:35140336

   Open questions at the time

   • Step of invasion that fails is not resolved
   • Molecular function during invasion unknown
   • Partial (proportion of merozoites) invasion failure not fully explained
4. 2022 Medium

   To determine why invasion fails, knockdown phenotypes linked CERLI2 to organelle formation: rhoptries became elongated and antigen processing was inhibited, implicating CERLI2 in rhoptry biogenesis and maturation rather than invasion motility alone.

   Evidence Inducible knockdown with microscopy and biochemical analysis of antigen processing in P. falciparum

   PMID:35140336

   Open questions at the time

   • Molecular basis of the morphology and processing defect unknown
   • Which antigens/proteases are affected not defined
   • Direct versus indirect role in processing unresolved
5. 2024 Medium

   Higher-resolution imaging refined the biogenesis defect, showing CERLI2 loss alters rhoptry neck morphology, distinguishing its phenotype from RON11 (single-rhoptry formation without structural change).

   Evidence Ultrastructure expansion microscopy (U-ExM) following loss-of-function in P. falciparum

   PMID:39292724

   Open questions at the time

   • Mechanistic link between a cytosolic bulb protein and neck morphology not established
   • Comparative context drawn from a different study
   • Single lab
6. 2025 Medium

   The upstream control of cerli2 expression was addressed, showing the AP2 factor PbSIP2 binds near the cerli2 locus during schizogony in P. berghei, placing cerli2 within a transcriptional program timed to organelle biogenesis.

   Evidence ChIP-seq in P. berghei during schizogony

   PMID:40117352

   Open questions at the time

   • Binding proximity does not prove functional regulation of cerli2 expression
   • Shown in P. berghei, not P. falciparum
   • Consequence of PbSIP2 loss on cerli2 not measured

• The molecular activity of CERLI2 and its direct binding partners at the rhoptry bulb membrane remain undefined, leaving open how a cytosolic-facing bulb protein controls rhoptry neck morphology and antigen processing.
• No enzymatic or biochemical activity assigned
• No experimentally validated direct protein partners
• No structural model of the protein