PFI1785w: A highly conserved protein associated with pregnancy associated malaria

Abstract

Pregnancy-associated malaria (PAM) is one of the severe forms of Plasmodium falciparum infection. The main antigen VAR2CSA is the target of vaccine development. However, the large size of VAR2CSA protein and its high degree of variability limit to the efficiency of the vaccination. Using quantitative mass spectrometry method, we detected and quantified proteotypic peptides from 5 predicted PAM associated proteins. Our results confirmed that PFI1785w is over-expressed in PAM samples. Then, we investigated PFI1785w variability among a set of parasite samples from various endemic areas. PFI1785w appear to be more conserved than VAR2CSA. PFB0115w, another PAM associated protein, seems also associated with the pathology. Further vaccination strategies could integrate other proteins in addition to the major VAR2CSA antigen to improve immune response to vaccination.

Fig 1. Skyline output and calibration range for GHTVDSELTTEDPVIQKK.

Retention time is displayed on x axis and intensity for each ion or fragment is displayed on y axis. Each parent ion and fragment is shown in a different colour. AUC corresponds to the integration of signal under the curve (A). Regression line is obtained using AUC from each concentration point.

Fig 2. Peptide concentration measured within calibration range of each peptide.

Peptide concentrations calculated by linear regression for each studied protein, y axis presents peptide concentration. Each dot represents one sample, and reference strains are displayed separately on the right of each plot (CSA+: CSA adhesion selected parasite strain, CSA-: non selected parasite strain). PAM samples and CSA+ parasite strains display a placental malaria like binding phenotype (in red), and UM samples and CSA- parasite strain display a uncomplicated malaria phenotype (in blue). PF14_0018, PFA_0410w, PFB0115w and PFI1785w are preferentially found in PAM like samples.

Fig 3. Geographic origin of the samples used for genomic studies of PFI1785w.

Fig 4. Alignment of PFI1785w sequence with mutation in pfi1785w observed in field isolates.

Alignment of PFI1785w protein sequences using the full length PFI1785w as a reference (1463004). Sequence names correspond to the position of the mutation found in genomic sequence. Mutation on PFI1785w gene (1,462,512 C->T) (12/33 sequences) and (1,463,271 C->T) (1/33 sequences) lead to amino acid changes in protein sequence on position 38 (Thr->Met) and 235 (Thr->Ile).

Fig 5. Secondary structure of PFI1785w predicted using Phyre 2 and predictive 3D structure of amino-acid 224–360.