The MB2 gene family of Plasmodium species has a unique combination of S1 and GTP-binding domains

Abstract

Background: Identification and characterization of novel Plasmodium gene families is necessary for developing new anti-malarial therapeutics. The products of the Plasmodium falciparum gene, MB2, were shown previously to have a stage-specific pattern of subcellular localization and proteolytic processing.

Results: Genes homologous to MB2 were identified in five additional parasite species, P. knowlesi, P. gallinaceum, P. berghei, P. yoelii, and P. chabaudi. Sequence comparisons among the MB2 gene products reveal amino acid conservation of structural features, including putative S1 and GTP-binding domains, and putative signal peptides and nuclear localization signals.

Conclusions: The combination of domains is unique to this gene family and indicates that MB2 genes comprise a novel family and therefore may be a good target for drug development.

Figure 1

Schematic diagram of the predicted translation products of six MB2 genes. The letters B, A and G label the respective domains of PfMB2. The boundaries of these domains are delimited by thin vertical lines. Shaded bars represent conserved regions, three of which, S1, A₁, and A₂ are labeled in PfMB2. Vertical lines interrupting the horizontal lines or contained within the boxes indicate regions containing repeated amino acid sequences. Numbers on the right indicate the number of amino acids in each product. Abbreviations: Pf, Plasmodium falciparum; Pk, P. knowlesi; Pg, P. gallinaceum; Py, P. yoelii; Pb, P. berghei and Pc, P. chabaudi.

Figure 2

Alignment of the predicted amino acids in the PfMB2 B domain with the amino-terminal domains of MB2 homologue translation products. Amino acids highlighted in black are conserved in all genes, those highlighted in gray are conserved in the majority of genes (at least four). A solid line underlines predicted signal peptides. A solid bracket above the Pf sequence delimits the antigenic region of PfMB2 [3]. A dotted line underlines the predicted S1 domain. A repeat region of PfMB2 is boxed. Alignment generated using the Clustal method (DNAStar) and manual alignment. Numbers in parenthesis indicate represented amino acids. Abbreviations are the same as in Figure 1.

Figure 3

Alignment of MB2 S1 domains with representative S1 domain sequences. Representative sequences containing an S1 domain are PNP/Ecoli: polyribonucleotide phosphorylase (PNPase), Escherichia coli [P05055/622–711], Stress/Li: protein similar to B. subtilis general stress protein 13, Listeria innocua [NP_471798/7–103], 30S_S1/Ll: 30S ribosomal protein S1, Lactococcus lactis lactis [NP_266994/195–312], S1/hu: ribosomal S1 protein, human [AAA97575/154–223], eIF2a/hu: eukaryotic initiation factor 2 alpha subunit, human [P05198/17–121], eIF2a/Pf: Putative eukaryotic initiation factor 2 alpha, Plasmodium falciparum [PF07_0017/20–138], identified from PlasmoDB database. MB2 S1 domains are included from six species: Pf = P. falciparum, Pk = P. knowlesi, Pg = P. gallinaceum, Pb = P. berghei, Py = P. yoelii, Pc = P. chabaudi. The secondary structure determined for PNPase [10] is represented above the alignment with a α helix indicated by a cylinder and β sheets indicated by thick lines. The structure predicted for PfMB2 is represented below the alignment. Black triangles indicate highly conserved residues identified by Bycroft et al., [10]. Asterisks indicate sequences identified by BLAST search with MB2 sequences. Alignment generated using the Clustal method (DNAStar). Similar amino acid residues are shaded.

Figure 4

Alignment of the PfMB2 A domain with the central domains of homologous MB2 translation products. Repeated amino acid sequences are boxed with a single repeat unit outlined with a dark box. Putative nuclear localization sequences are underlined with a solid line. Putative cell-surface retention sequences are underlined with a broken line. Alignment generated using the Clustal method (DNAStar) and manual alignment. Numbers in parenthesis indicate represented amino acids. Abbreviations are the same as in Figure 2.

Figure 5

Alignment of carboxyl-terminal G domains of homologous MB2 translation products. The three G domain consensus sequences are underlined. Repeated motifs are boxed with a single motif outlined by a dark box. Generated by Clustal method (DNAStar). Numbers in parenthesis indicate represented amino acids. Abbreviations are the same as in Figure 2.

Figure 6

Alignment of Plasmodium falciparum G domains. Sequences were obtained from the PlasmoDB database. Amino acids included in alignment are PfMB2 [989–1232] and four annotated P. falciparum contigs from the PlasmoDB database: PFO8_0018 [650–959], translation initiation factor-like protein; MAL61.73 [390–638], putative translation initiation factor, IF-2; PF13_0069 [207–403], putative translation initiation factor, IF-2; PFL1590c [41–340], putative elongation factor G. The three G domain consensus motifs are underlined. Generated by Clustal method (DNAStar) and manual alignment. Abbreviations are the same as in Figure 2.