Mutant/mutation
The mutant lacks expression of SBP1 (and in addition it expresses GFP under control of the eef1a promoter).

Protein (function)
SBP1 of P. falciparum is a Maurer's cleft protein and is part of the trafficking machinery that trafics PfEMP1 to the surface of infected red blood cells. SBP1 is a PEXEL-negative protein. Infected red blood cells with P. falciparum parasites lacking expression of SBP1 fail to cytoadhere to endothelial receptors of blood vessels, such as CD36 and ICAM1.

Phenotype
While no phenotypic differences were observed between the gene-deletion mutants and wild-type (wt) parasites during development in the mosquito or in the liver, blood stages of the mutants exhibited an attenuated phenotype in mice. While wt-infected C57B/6 mice died 7–9 days post infection as a result of complications typical for experimental cerebral malaria, PbΔsbp1-infected mice did not develop experimental cerebral malaria but died from hyperparasitemia 32–45 days post infection, respectively. A similar attenuation was also observed in infections in Balb/c mice. The parasitemia in the PbΔsbp1-infected mice was comparable to that of wt during the initial 2 days of infection, but was reduced compared with wt thereafter. Mutant parasites were predominantly found in reticulocytes throughout the course of infection, whereas virulent wt parasites were found in erythrocytes in the later course of infection.
In addition, mice infected with the PbΔsbp1 mutants showed a 3.6-fold increase in schizonts in the peripheral blood circulation compared to wt infections, respectively, indicating reduced sequestration of RBCs infected with mutant schizonts.
PbΔsbp1 parasites showed strongly reduced accumulation in the adipose tissue and lungs compared with wt, which is typical for a loss of CD36-mediated sequestration. Conversely, significantly increased accumulation of parasites was detected in the spleens of mice infected with PbΔsbp1 mutants. Higher accumulation in the spleen of non-sequestered schizonts has been attributed to increased removal of non-sequestering schizonts by the spleen.
Binding to mouse CD36 was significantly lower in PbΔsbp1 schizonts compared with wt schizonts with both plate-coated CD36 or CD36 expressed on CHO-745 cells.

Additional information
While the overall amino-acid similarity between the SBP1 of P. berghei and P. falciparum was rather low, the architecture of the protein features was similar and both proteins lack a PEXEL motif. In addition, three other findings indicated that these proteins are indeed orthologues. Firstly, the phylogenetic trees of these proteins are topologically concordant with the species tree of malaria parasites; secondly, a jackhmmer search arrived at the same proteins originally detected by our similarity searches; and finally, a re-examination of the genomic location revealed that the genes encoding SBP1 orthologues are in fact syntenic.

Immunofluorescence assays with these sera showed that PbSBP1 was exported into P. berghei iRBCs where they were found in multiple discrete foci.

By introducing P. falciparum sbp1 gene into PbΔsbp1 evidence is presented that P. falciparum SBP1 complements the function of P. berghei SBP1: the growth-, sequestration- and virulence phenotype were (partly) restored in the complemented mutant.

Other mutants
RMgm-1465: An independent mutant lacking expression of SBP1 (and expressing mCherry and Luciferase)