PF3D7_0424400

surface-associated interspersed protein 4.2 (SURFIN 4.2)

Annotated: 2026-09-07

28 papers in source corpus 8 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SURF4.2 (PF3D7_0424400) is a Plasmodium falciparum type I transmembrane protein that operates at two stages of the intraerythrocytic cycle: it is exported to the surface of infected erythrocytes during blood-stage growth and relocalizes to the merozoite apex for invasion (PMID:15939796). During export, SURF4.2 traffics through Maurer's clefts to the infected-RBC surface by a PEXEL-independent route in which the transmembrane region is necessary and sufficient for delivery to the clefts, while the N-terminal sequence remains uncleaved (PMID:21616162, PMID:17255224). Onward transport from Maurer's clefts to the erythrocyte surface then depends on the cytoplasmic tryptophan-rich (WR) domain (PMID:26865830), which drives detergent-resistant membrane-skeleton association (PMID:21616162); the second WR domain (WRD2) binds the RBC membrane skeleton directly, engaging inside-out vesicles, F-actin and spectrin with sub-micromolar to low-micromolar affinity (PMID:28320404). In merozoites SURF4.2 localizes to the rhoptry neck and is secreted into the parasitophorous vacuole, where it assembles into the SURGE complex with the rhoptry neck protein RON4 and GLURP; its N-terminal extracellular cysteine-rich domain mediates RBC membrane binding, and antibodies against the extracellular domain partially inhibit merozoite invasion (PMID:30092030). Whether SURF4.2 has a role in rosette formation is a surface-antibody-based observation that was not functionally validated (PMID:29459776).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps

2005 Medium
Establishing that SURF4.2 reaches the infected-erythrocyte surface answered whether this protein is a parasite-derived surface antigen co-trafficked with known virulence proteins.

Evidence Surface trypsinization plus mass spectrometry and IFA co-localization with PfEMP1 and RIFIN on live infected erythrocytes

PMID:15939796
Open questions at the time
- Trafficking route and domain requirements not defined
- Functional role at the surface not tested
2007 Low
Detecting SURF4.2 in Maurer's clefts identified the intermediate trafficking compartment on the path to the erythrocyte surface.

Evidence Indirect immunofluorescence with Giemsa staining and transmission electron microscopy on infected erythrocytes

PMID:17255224
Open questions at the time
- Single IFA method, no functional consequence tested
- Does not resolve how the protein enters or exits the clefts
2011 Medium
Domain-mapping resolved that SURF4.2 export is PEXEL-independent and driven by its transmembrane region, distinguishing it from canonical PEXEL-motif exported proteins.

Evidence GFP-fusion deletion/replacement constructs in transgenic parasites with IFA and Triton X-100 fractionation Western blotting

PMID:21616162
Open questions at the time
- Mechanism recognizing the TM region for export not identified
- Onward step to the surface not addressed
2011 Low
Biochemical fractionation linked the cytoplasmic WR domain to detergent-resistant/membrane-skeleton association, hinting at how SURF4.2 anchors at the erythrocyte cortex.

Evidence Triton X-100 fractionation and Western blotting of recombinant SURF4.2 constructs with and without the WR domain

PMID:21616162
Open questions at the time
- Single biochemical fractionation, no direct binding partner shown
- Functional consequence not demonstrated
2015 Medium
Functional dissection showed the cytoplasmic WR-containing region is required for the final step of transport from Maurer's clefts to the iRBC surface, defining a two-stage export mechanism.

Evidence Transgenic parasites with/without the intracellular region, proteinase K surface accessibility assay and IFA

PMID:26865830
Open questions at the time
- Molecular partners at the surface delivery step not identified
- Does not quantify surface abundance or virulence impact
2017 High
In vitro binding assays established a direct molecular interaction between SURF4.2 and the RBC membrane skeleton, providing the biochemical basis for its cortical anchoring.

Evidence Recombinant WRD2 binding to inside-out vesicles, F-actin co-sedimentation, and ELISA-based spectrin binding with quantified affinities

PMID:28320404
Open questions at the time
- Binding not demonstrated in the native cellular context
- Physiological consequence of skeleton binding for the host cell not established
2018 Medium
Identifying rhoptry-neck localization and the SURGE complex extended SURF4.2's role beyond surface display to invasion, defining its partners and an invasion-relevant binding domain.

Evidence Reciprocal co-IP/MS identifying RON4 and GLURP, immuno-EM localization, and antibody-based invasion inhibition assays

PMID:30092030
Open questions at the time
- Stoichiometry and assembly order of the SURGE complex unknown
- Erythrocyte receptor for the CRD not identified
- Only partial invasion inhibition observed
2018 Low
Serological profiling confirmed SURF4.2 is an immune target at the infected-cell surface and raised the possibility of a rosetting role.

Evidence Peptide-array serology with patient sera and rosetting-rate assessment

PMID:29459776
Open questions at the time
- Rosette role explicitly not functionally validated
- Indirect serological inference of surface exposure
2019 Low
Tagged mini-SURF4.2 confirmed the N-terminus is not cleaved during export and that Maurer's-cleft targeting elements are shared with the paralog SURFIN4.1.

Evidence Myc-tagged mini-SURF4.2 transgenic parasites with anti-Myc IFA

PMID:31028841
Open questions at the time
- Single IFA readout secondary to a SURFIN4.1 study
- Does not identify the export receptor for the shared signal

Open questions

Synthesis pass · forward-looking unresolved questions

The erythrocyte surface receptor engaged by the SURF4.2 extracellular cysteine-rich domain during invasion, and the causal contribution of its membrane-skeleton binding to host-cell remodeling or rosetting, remain undefined.
No identified host receptor for the CRD
SURGE complex assembly mechanism unresolved
Rosetting role not functionally tested

Mechanism profile

Synthesis pass · controlled-vocabulary classification

Partners

GLURP (GLUTAMATE-RICH PROTEIN) [#6]RBC F-ACTIN [#5]RBC INSIDE-OUT MEMBRANE VESICLES [#5]RBC SPECTRIN [#5]RON4 (RHOPTRY NECK PROTEIN) [#6]

Complex memberships

SURGE complex (SURF4.2 with RON4 and GLURP) [#6]

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus

Year	Finding	Method	Journal	Conf	PMIDs
2005	SURF4.2 (SURFIN4.2) protein was identified on the surface of live P. falciparum-infected erythrocytes (IEs) by mass spectrometric analysis of trypsin-cleaved peptides, and was found co-transported with PfEMP1 and RIFIN to the IE surface. It also accumulated in the parasitophorous vacuole and was present as an amorphous cap at the apex of released merozoites.	Mass spectrometric analysis of surface-trypsinized peptides from live IEs; immunofluorescence assay; co-localization with PfEMP1 and RIFIN	The Journal of experimental medicine	Medium	15939796
2007	SURF4.2 (SURFIN4.2) was detected in Maurer's clefts of P. falciparum-infected erythrocytes, alongside PfEMP1 and RIFIN, by immunofluorescence assay combined with Giemsa staining, placing it in this trafficking compartment.	Indirect immunofluorescence assay combined with Giemsa staining and transmission electron microscopy	The American journal of tropical medicine and hygiene	Low	17255224
2011	SURF4.2 trafficking to the infected RBC and Maurer's clefts is PEXEL-independent: the transmembrane (TM) region is necessary and sufficient for trafficking, whereas two PEXEL-like sequences, the N-terminal cysteine-rich domain, the variable region, and the WR domain are not required for this trafficking step. A mini-SURF4.2 containing 50 amino acids upstream of TM, the TM itself, and part of the cytoplasmic region was sufficient for localization to the iRBC and Maurer's clefts.	Transgenic parasite lines expressing GFP-fused SURFIN4.2 deletion/replacement constructs; immunofluorescence assay; Western blotting with Triton X-100 fractionation	Parasitology international	Medium	21616162
2011	The cytoplasmic WR domain of SURF4.2 is associated with Triton X-100 insolubility: a recombinant SURF4.2 containing the WR domain was more abundantly detected in the Triton X-100-insoluble fraction compared to one without the WR domain, suggesting the WR domain influences membrane skeleton association or detergent-resistant complex formation.	Western blotting of Triton X-100 fractionated transgenic parasite lysates	Parasitology international	Low	21616162
2015	The intracellular region of SURF4.2 containing the tryptophan-rich (WR) domain is required for transport from Maurer's clefts to the iRBC surface: transgenic parasites expressing SURF4.2 without the intracellular WR-containing region were exported to Maurer's clefts but were not efficiently cleaved by surface proteinase K treatment, whereas those retaining the intracellular region were surface-exposed.	Transgenic parasite lines expressing modified SURFIN4.2 with/without intracellular region; proteinase K surface treatment of iRBC; immunofluorescence assay	Tropical medicine and health	Medium	26865830
2017	The second tryptophan-rich domain (WRD2) of SURF4.2 directly binds the red blood cell membrane skeleton: recombinant WRD2 bound inside-out vesicles (IOVs) of RBCs with Kd in the range of 0.26–0.68 µM, F-actin with Kd = 5.16 µM, and spectrin with Kd = 0.51 µM.	In vitro binding assay with inside-out vesicles; actin spin-down assay; ELISA-based spectrin binding assay; recombinant protein expression; transgenic parasite fluorescence microscopy	Malaria journal	High	28320404
2018	SURF4.2 is present in the neck of the rhoptries of P. falciparum merozoites, is secreted into the parasitophorous vacuole, and is shed into culture supernatant upon schizont rupture. SURF4.2 forms a protein complex (named SURGE) with the rhoptry neck protein RON4 and the Glutamate Rich Protein GLURP, as shown by immunoprecipitation followed by mass spectrometry. The N-terminal cysteine-rich domain (CRD) of SURF4.2 mediates binding to the RBC membrane. Polyclonal antibodies against the extracellular domain (including CRD) of SURF4.2 partially inhibit merozoite invasion.	Immunoprecipitation followed by mass spectrometry (co-IP/MS); antibody localization by immunofluorescence and immunoelectron microscopy; invasion inhibition assay with polyclonal antibodies	PloS one	Medium	30092030
2019	N-terminally Myc-tagged mini-SURF4.2 (containing the N-terminal region, TM region, and cytoplasmic region) was detected at Maurer's clefts by anti-Myc antibody staining, indicating that the N-terminal sequence of SURF4.2 is not cleaved during export and that elements required for export to Maurer's clefts are conserved between SURFIN4.1 and SURFIN4.2.	Transgenic parasite lines expressing Myc-tagged mini-SURFIN4.2; immunofluorescence assay with anti-Myc antibody	Parasitology international	Low	31028841
2018	Naturally acquired antibodies from children with malaria react with SURF4.2 at the parasitized RBC surface, and data indicate SURF4.2 may have a function during rosette formation, though this was not formally validated in the study.	Serological profiling with peptide arrays; assessment of rosetting rate and surface reactivity using patient sera	Scientific reports	Low	29459776

Source papers

Stage 0 corpus · 28 papers · ranked by NIH iCite citations

Year	Title	Journal	Citations	PMID
2008	Exported proteins required for virulence and rigidity of Plasmodium falciparum-infected human erythrocytes.	Cell	410	18614010
2005	SURFIN is a polymorphic antigen expressed on Plasmodium falciparum merozoites and infected erythrocytes.	The Journal of experimental medicine	144	15939796
2012	Population genomic scan for candidate signatures of balancing selection to guide antigen characterization in malaria parasites.	PLoS genetics	134	23133397
2014	Surface antigens of Plasmodium falciparum-infected erythrocytes as immune targets and malaria vaccine candidates.	Cellular and molecular life sciences : CMLS	120	24691798
2016	Genome-scale comparison of expanded gene families in Plasmodium ovale wallikeri and Plasmodium ovale curtisi with Plasmodium malariae and with other Plasmodium species.	International journal for parasitology	67	27392654
2013	Variant surface antigens of malaria parasites: functional and evolutionary insights from comparative gene family classification and analysis.	BMC genomics	62	23805789
2010	Allele frequency-based and polymorphism-versus-divergence indices of balancing selection in a new filtered set of polymorphic genes in Plasmodium falciparum.	Molecular biology and evolution	58	20457586
2008	SURFIN4.1, a schizont-merozoite associated protein in the SURFIN family of Plasmodium falciparum.	Malaria journal	33	18593471
2008	MAAP: malarial adhesins and adhesin-like proteins predictor.	Proteins	32	17879344
2006	Multi-character population study of the vir subtelomeric multigene superfamily of Plasmodium vivax, a major human malaria parasite.	Molecular and biochemical parasitology	26	16730808
2011	PEXEL-independent trafficking of Plasmodium falciparum SURFIN4.2 to the parasite-infected red blood cell and Maurer's clefts.	Parasitology international	23	21616162
2020	Global Repertoire of Human Antibodies Against Plasmodium falciparum RIFINs, SURFINs, and STEVORs in a Malaria Exposed Population.	Frontiers in immunology	21	32477363
2012	The N-terminal segment of Plasmodium falciparum SURFIN4.1 is required for its trafficking to the red blood cell cytosol through the endoplasmic reticulum.	Parasitology international	20	23287798
2018	Antibodies in children with malaria to PfEMP1, RIFIN and SURFIN expressed at the Plasmodium falciparum parasitized red blood cell surface.	Scientific reports	19	29459776
2007	Characterization of Maurer's clefts in Plasmodium falciparum-infected erythrocytes.	The American journal of tropical medicine and hygiene	15	17255224
2018	SURGE complex of Plasmodium falciparum in the rhoptry-neck (SURFIN4.2-RON4-GLURP) contributes to merozoite invasion.	PloS one	14	30092030
2017	Tryptophan-rich domains of Plasmodium falciparum SURFIN4.2 and Plasmodium vivax PvSTP2 interact with membrane skeleton of red blood cell.	Malaria journal	11	28320404
2015	The Cytoplasmic Region of Plasmodium falciparum SURFIN4.2 Is Required for Transport from Maurer's Clefts to the Red Blood Cell Surface.	Tropical medicine and health	10	26865830
2011	Stable allele frequency distribution of the polymorphic region of SURFIN(4.2) in Plasmodium falciparum isolates from Thailand.	Parasitology international	10	22212242
2021	Plasmodium falciparum SURFIN4.1 forms an intermediate complex with PTEX components and Pf113 during export to the red blood cell.	Parasitology international	9	33901679
2017	Selections, frameshift mutations, and copy number variation detected on the surf 4.1 gene in the western Kenyan Plasmodium falciparum population.	Malaria journal	6	28253868
2022	Plasmodium falciparum merozoite invasion ligands, linked antimalarial resistance loci and ex vivo responses to antimalarials in The Gambia.	The Journal of antimicrobial chemotherapy	5	35904009
2019	Multiple charged amino acids of Plasmodium falciparum SURFIN4.1 N-terminal region are important for efficient export to the red blood cell.	Parasitology international	5	31028841
2012	Positive diversifying selection on the Plasmodium falciparum surf4.1 gene in Thailand.	Tropical medicine and health	5	23264727
2025	Exploring the P. falciparum antigens associated with reduced risk of malaria in pregnancy.	Frontiers in immunology	2	40726979
2024	Variable Surface Antigens of Plasmodium falciparum: Protein Families with Divergent Roles.	Protein and peptide letters	1	38910420
2017	Knockdown of the Plasmodium falciparum SURFIN4.1 antigen leads to an increase of its cognate transcript.	PloS one	1	28800640
2025	Method for deletion of variant surface antigen genes at subtelomeric region of Plasmodium falciparum.	Parasitology international	0	40562206