Functional Analysis of the Exported Type IV HSP40 Protein PfGECO in Plasmodium falciparum Gametocytes

Abstract

During Plasmodium falciparum infection, host red blood cell (RBC) remodeling is required for the parasite's survival. Such modifications are mediated by the export of parasite proteins into the RBC that alter the architecture of the RBC membrane and enable cytoadherence. It is probable that some exported proteins also play a protective role against the host defense response. This may be of particular importance for the gametocyte stage of the life cycle that is responsible for malaria transmission, since the gametocyte remains in contact with blood as it proceeds through five morphological stages (I to V) during its 12-day maturation. Using microarray analysis, we identified several genes with encoded secretory or export sequences that were differentially expressed during early gametocytogenesis. One of these, PfGECO, encodes a predicted type IV heat shock protein 40 (HSP40) that we show is expressed in gametocyte stages I to IV and is exported to the RBC cytoplasm. HSPs are traditionally induced under stressful conditions to maintain homeostasis, but PfGECO expression was not increased upon heat shock, suggesting an alternate function. Targeted disruption of PfGECO indicated that the gene is not essential for gametocytogenesis in vitro, and quantitative reverse transcriptase PCR (RT-PCR) showed that there was no compensatory expression of the other type IV HSP40 genes. Although P. falciparum HSP40 members are implicated in the trafficking of proteins to the RBC surface, removal of PfGECO did not affect the targeting of other exported gametocyte proteins. This work has expanded the repertoire of known gametocyte-exported proteins to include a type IV HSP40, PfGECO.

Transposon mutagenesis identifies genes essential for Plasmodium falciparum gametocytogenesis

“…2C). In agreement with these results, the putatively disrupted gene in IGM 2D3, pfl2550w, was knocked out independently and found to produce mature gametocytes (37). Thus, we believe that IGM 2D3 carries a second site mutation that accounts for the loss of gametocytogenesis.…”

Sexual development in Plasmodium parasites: knowing when it's time to commit

“…This suggests that these genes do have a specific role in some stage of gametocyte development. However, two of the genes identified in this study, pfgeco and P. falciparum LCCL domain-containing protein 2 (pfccp2; PF3D7_1455800/PF14_0532) have been successfully disrupted previously in other studies with no effect on gametocytogenesis, despite their expression in gametocytes 55,56 . The remaining genes identified thus require further validation to confirm whether they are in fact required for gametocyte development.…”

Dissection of Structural and Functional Requirements That Underlie the Interaction of ERdj3 Protein with Substrates in the Endoplasmic Reticulum

“…It is noteworthy that for other DnaJ family members, the converse is true; stimulating the ATPase of an Hsp70 is critical, but substrate binding is not (37). More recently, a group of type IV family members have been identified that possess a J domain without the highly conserved HPD consensus sequence (13,38,39), arguing that the importance of these two functions varies by the role of the specific DnaJ family member.…”