RPS4

PF3D7_1105400 (S4) is a constituent ribosomal protein of the small (40S) subunit of the Plasmodium falciparum 80S ribosome, established through high-resolution structural characterization of the intact translation machinery (PMID:24913268, PMID:40825879). It is resolved as a structural component of the 40S subunit across multiple cryo-EM reconstructions of ribosomes captured in distinct functional states during translation (PMID:26432834), and it is present in the natively assembled, actively translating ribosome imaged in situ within infected erythrocytes (PMID:40825879). The same structural studies define the P. falciparum ribosome as the target of antimalarials including emetine, which blocks translocation at the small-subunit E-site (PMID:24913268), and mefloquine, which binds the large-subunit GTPase-associated centre (PMID:28288098). Beyond its membership in the 40S subunit as visualized in these structures, no experiment in the available corpus has directly interrogated the individual function, specific interactions, or translational contribution of S4 itself.

1. 2014 Medium

   Before this work the molecular architecture of the P. falciparum ribosome was unknown; determining the 80S structure placed S4 as a defined structural component of the 40S small subunit and revealed how emetine blocks translocation at the small-subunit E-site.

   Evidence Cryo-EM structure determination of the intact 80S ribosome at 3.2 Å resolution

   PMID:24913268

   Open questions at the time

   • No functional experiment isolates S4's individual contribution to translation
   • S4-specific interactions within the 40S subunit not dissected
   • Role inferred solely from complex membership
2. 2015 Medium

   To understand the ribosome across the translation cycle, multi-state reconstructions were obtained, positioning S4 structurally within the 40S subunit in several functional conformations rather than a single static state.

   Evidence Five sub-nanometer cryo-EM reconstructions from blood-stage schizonts with flexible fitting and atomic model building

   PMID:26432834

   Open questions at the time

   • No experiment interrogates whether S4 changes role across the functional states
   • S4 conformational dynamics not analyzed individually
3. 2017 Medium

   To validate the ribosome as an antimalarial target, the mefloquine-bound structure and binding-site mutagenesis confirmed drug action at the GTPase-associated centre, with S4 again resolved as part of the 40S subunit in the complex.

   Evidence Cryo-EM at 3.2 Å plus site-directed mutagenesis of binding-site residues with resistance phenotype readout

   PMID:28288098

   Open questions at the time

   • Drug-binding and mutagenesis concern the large-subunit GTPase-associated centre, not S4
   • No functional role attributed to S4
4. 2025 Medium

   To move from purified particles to physiological context, in situ cryo-ET captured the native ribosome during active translation inside infected cells, confirming S4's membership in the physiologically assembled, translating 40S subunit.

   Evidence In situ cryo-electron tomography at high resolution inside infected erythrocytes, eight structures across elongation states

   PMID:40825879

   Open questions at the time

   • Still no isolation of S4-specific function or interactions
   • No perturbation of S4 to test its necessity for elongation

• What is the individual functional contribution of S4 to 40S assembly, mRNA/tRNA handling, or translation fidelity, and what are its specific molecular partners beyond bulk 40S membership?
• No genetic or biochemical perturbation of S4 reported
• No S4-specific interaction map
• No essentiality or knockdown data for S4 in the corpus