Disruption of the rhomboid motif impairs TRAP cleavage.

<p>(A) Primary structure of TRAP expressed in TRAP-VAL and TRAP-FFF mutants, with the point mutations introduced to disrupt the putative rhomboid substrate motif indicated above each transmembrane domain. (B) Western blot analysis of recombinant control TRAP-rWT (rWT) and rhomboid cleavage mutant salivary gland sporozoites TRAP-VAL and TRAP-FFF (VAL and FFF) probed with TRAP anti-repeat antisera. As a loading control the bottom half of the membrane was probed with mAb 3D11 which recognizes the repeat region of CSP. (C) Pulse-chase metabolic labeling of TRAP-rWT and rhomboid cleavage site mutants. Salivary gland sporozoites were metabolically labeled for 1 hr and either placed on ice for 4 hrs (Time = 0) or chased for 4 hrs (Time = 4). Sporozoites were then centrifuged and TRAP was immunoprecipitated from either the pellet (P) or supernatant (S) using anti-repeat antisera and analyzed by SDS-PAGE and autoradiography. Molecular weight markers shown on left of top panel. Top panel: 6 day exposure. Bottom panel: 14 day exposure, arrows show location of processed VAL and FFF mutant TRAP. (D) Immunofluorescence analysis of surface TRAP staining in TRAP-rWT and rhomboid cleavage site mutants. Shown are representative fluorescence and phase contrast images of the TRAP staining pattern after fixation with paraformaldehyde. Microscope and camera settings were identical for all photographs. (E) Box plot of fluorescence intensity of TRAP surface staining in TRAP-rWT and rhomboid cleavage site mutants. Unpermeabilized sporozoites were stained with anti-TRAP repeat antisera and intensity of staining was measured using NIS Elements software. Identical camera and microscope settings were used for all measurements. Boxes contain 50% of the data around its median (black line in box). Whiskers show the range of data within the 10^th and 90^th percentiles and outliers are shown individually. Results are pooled from 2 to 4 independent experiments. There was a statistically significant difference in staining intensity between TRAP-rWT and TRAP-VAL sporozoites (p<.0001) and between TRAP-rWT and TRAP-FFF sporozoites (p<.0001).</p

In vivo infectivity of TRAP mutant sporozoites as determined by prepatent period.

<p>In vivo infectivity of TRAP mutant sporozoites as determined by prepatent period.</p

TRAP-DMut sporozoites are severely impaired in gliding motility and host cell invasion.

<p>(A) Gliding motility of TRAP-JMD and TRAP-DMut sporozoites. Salivary gland sporozoites were incubated on slides for 1 hr and trails were visualized and counted. The percentage of sporozoites with and without trails is shown in the pie charts. For those sporozoites associated with trails, the number of circles produced by each sporozoite was counted and shown is their distribution for each parasite line. Over 100 sporozoites per well were counted and shown are the means of triplicate wells ± SD. (B) Representative images of the types of trails produced by each mutant. (C) Hepatocyte invasion. Salivary gland sporozoites were incubated with Hepa 1–6 cells for 1 hr, fixed and stained with a double staining assay that distinguishes extracellular and intracellular sporozoites. Percent invasion was determined and shown are the means ± SD of duplicate wells. All experiments were performed at least twice and shown is a representative experiment.</p

Sporozoite numbers and localization in mosquitoes infected with control and mutant parasites.

<p>*Mosquitoes were infected with the indicated parasite clones and midguts, hemolymph and salivary glands were harvested from 15 mosquitoes at days 14, 16 and 18 post-infective blood meal respectively, pooled and sporozoites were counted. Shown are the means of three independent experiments ± SD.</p>#<p>Sporozoites in the supernatant and pellet of trypsin-treated salivary glands were counted and the percentage inside was calculated. There were 15 mosquitoes per group. This experiment was performed twice with similar results.</p

Impaired TRAP processing leads to aberrant gliding motility.

<p>(A) Gliding motility of rhomboid cleavage site mutants. Salivary gland sporozoites were incubated on slides for 1 hr and trails were visualized and counted. The percentage of sporozoites with and without trails is shown in the pie charts. For those sporozoites associated with trails, the number of circles produced by each sporozoite was counted and shown is their distribution for each parasite line. Asterisks indicate that none of the TRAP-VAL and TRAP-FFF mutants were associated with over 50 circles. Over 100 sporozoites per well were counted and shown are the means of triplicate wells ± SD. (B) Live imaging of gliding motility of rhomboid cleavage site mutant sporozoites. Sporozoites were observed and recorded using a Leica laser scanning confocal microscope. Time lapse images of sporozoites gliding on glass bottom dishes are shown with the maximum intensity projection on the right. (C) For each parasite line the average speed of ten sporozoites was determined for 60 s. All experiments were performed at least twice and a representative experiment is shown.</p

Impaired TRAP processing of rhomboid cleavage site mutants leads to impaired host cell invasion.

<p>(A) In vitro invasion. Salivary gland sporozoites were incubated with Hepa 1–6 cells and fixed after 1 hr (data on left) or 6 hrs (data on right). Cells fixed after 1 hr were stained with a double staining assay that distinguishes between extracellular and intracellular sporozoites and the percent of total sporozoites that were intracellular was determined (left axis). Cells fixed after 6 hrs were stained with UIS4 antisera to determine the number of sporozoites that had entered in a vacuole (right axis). For both experiments at least 50 fields per well were counted and shown are the means ± SD of duplicate wells. (B) Kinetics of entry into hepatocytes. Salivary gland sporozoites were incubated with Hepa 1–6 cells for 15, 30 and 45 mins before being washed, fixed and stained with a double-staining assay that distinguishes extracellular and intracellular sporozoites. Shown is the percent of total sporozoites that were in the process of entering host cells, i.e. partially inside and partially outside. 50 fields per coverslip were counted and the means of duplicates ±SD are shown. (C) EEF development. Salivary gland sporozoites were added to Hepa 1,6 cells and incubated for 48 hrs at which time they were fixed and stained. The number of EEFs in 50 fields per coverslip were counted and shown are the means ± SD of duplicate wells. (D) Cell traversal. Salivary gland sporozoites were incubated with Hepa 1,6 cells for 1 hr, in the presence of the nucleic acid dye TOTO-1. Controls were pre-incubated and kept in the presence of cytochalasin D (CD), which inhibits motility. The number of TOTO-1 positive cells in 50 fields was counted and the means ±SD of duplicate wells are shown. All experiments were performed at least twice and representative experiments are shown.</p

TRAP is proteolytically processed and shed from the sporozoite surface by a serine protease.

<p>(A) Primary Structure of TRAP: Shown are the extracellular adhesive domains, namely the A-domain and the type I thrombospondin repeat (TSR), as well as the repeat region, the juxtamembrane region (JMD), the transmembrane domain (TM) and cytoplasmic tail (CT). Anti-TRAP antibodies used in this study recognize either the repeat region (α-Rep) or the cytoplasmic tail of TRAP (α-CT). (B) Pulse-chase metabolic labeling and TRAP immunoprecipitation using anti-repeat or anti-cytoplasmic tail antisera. Salivary gland sporozoites were metabolically labeled and placed on ice for 2 hrs (Time = 0) or chased at 28°C for 2 hrs (Time = 2). Sporozoites were then centrifuged and TRAP was immunoprecipitated from either the pellet (P) or supernatant (S) using antibodies against the repeat region of TRAP (left panel) or antibodies against the cytoplasmic tail (right panel) and analyzed by SDS-PAGE and autoradiography. Supernatants from control sporozoites kept on ice did not contain any TRAP (data not shown). (C) Effect of protease inhibitors on TRAP cleavage. Salivary gland sporozoites were metabolically labeled and chased at 28°C for 2 hrs in the presence of the indicated protease inhibitors. Sporozoites were then centrifuged and TRAP was immunoprecipitated from either the pellet (P) or supernatant (S) using anti-repeat antisera and analyzed by SDS-PAGE and autoradiography. The following inhibitors were used: 10 µM E64, 1 mM PMSF, 1 µM pepstatin (Pep), 0.3 µM aprotinin (Apr), 100 µM 3,4 DCI, 100 µM TLCK, 75 µM leupeptin (Leu), and 5 mM EDTA. (D) Effect of protease inhibitors on gliding motility. Salivary gland sporozoites were pre-incubated with the indicated protease inhibitors and then added to slides in the continued presence of the inhibitor for 1 hr at 37°C. Sporozoite trails were visualized and the number of sporozoites with and without trails was counted. Inhibition of motility was calculated based on the motility of sporozoites pre-treated with media alone. Each inhibitor was tested in triplicate and 50 fields per well were counted. The means ± SD are shown. DCI-R indicates that DCI was replenished every 20 min. All inhibitors were tested in at least two independent experiments however DCI and PMSF were tested in 3 or more independent experiments. A representative experiment is shown.</p

ROM4 is expressed on the sporozoite surface and antibodies against the extracellular tail of ROM4 inhibit hepatocyte invasion.

<p>(A) Western blot analysis of <i>P. berghei</i> erythrocytic stage schizont lysate (sch) and salivary gland sporozoites (spz) probed with anti-PfROM4 C-terminal IgG. Molecular weight markers are in kDa. (B) Immunofluorescence of <i>P. berghei</i> salivary gland sporozoites fixed with cold methanol and stained with anti-CSP antibodies and anti-PfROM4 C-terminal IgG.</p

Transcript expression analysis of <i>phist</i> and <i>resa-like</i> genes in 4 <i>P</i>. <i>falciparum</i> isolates.

<p>The transcript levels of select <i>phist</i> and <i>resa-like</i> genes in 4 isolates of <i>P</i>. <i>falciparum</i>, NF54, Dd2, HB3 and IT4, were compared by real time PCR using cDNA prepared from late schizont stage parasites. Transcript expression was normalized to the expression of the control gene <i>arginyl tRNA synthetase</i> (<i>PFL0900c</i>). In the schematic depiction of <i>phist</i> and <i>resa-like</i> genes, yellow represents the signal sequence, and red represents the PEXEL/HT motif.</p

The <i>Plasmodium</i> PHIST and RESA-Like Protein Families of Human and Rodent Malaria Parasites

<div><p>The <i>phist</i> gene family has members identified across the <i>Plasmodium</i> genus, defined by the presence of a domain of roughly 150 amino acids having conserved aromatic residues and an all alpha-helical structure. The family is highly amplified in <i>P</i>. <i>falciparum</i>, with 65 predicted genes in the genome of the 3D7 isolate. In contrast, in the rodent malaria parasite <i>P</i>. <i>berghei</i> 3 genes are identified, one of which is an apparent pseudogene. Transcripts of the <i>P</i>. <i>berghei phist</i> genes are predominant in schizonts, whereas in <i>P</i>. <i>falciparum</i> transcript profiles span different asexual blood stages and gametocytes. We pursued targeted disruption of <i>P</i>. <i>berghei phist</i> genes in order to characterize a simplistic model for the expanded <i>phist</i> gene repertoire in <i>P</i>. <i>falciparum</i>. Unsuccessful attempts to disrupt <i>P</i>. <i>berghei PBANKA_114540</i> suggest that this <i>phist</i> gene is essential, while knockout of <i>phist PBANKA_122900</i> shows an apparent normal progression and non-essential function throughout the life cycle. Epitope-tagging of <i>P</i>. <i>falciparum</i> and <i>P</i>. <i>berghei phist</i> genes confirmed protein export to the erythrocyte cytoplasm and localization with a punctate pattern. Three <i>P</i>. <i>berghei</i> PEXEL/HT-positive exported proteins exhibit at least partial co-localization, in support of a common vesicular compartment in the cytoplasm of erythrocytes infected with rodent malaria parasites.</p></div