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A malaria membrane skeletal protein is essential for normal morphogenesis, motility, and infectivity of sporozoites.

Khater EI, Sinden RE, Dessens JT - J. Cell Biol. (2004)

Bottom Line: Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion.We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites.These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Imperail College London, London SW7 2AZ, England, UK.

ABSTRACT
Membrane skeletons are structural elements that provide mechanical support to the plasma membrane and define cell shape. Here, we identify and characterize a putative protein component of the membrane skeleton of the malaria parasite. The protein, named PbIMC1a, is the structural orthologue of the Toxoplasma gondii inner membrane complex protein 1 (TgIMC1), a component of the membrane skeleton in tachyzoites. Using targeted gene disruption in the rodent malaria species Plasmodium berghei, we show that PbIMC1a is involved in sporozoite development, is necessary for providing normal sporozoite cell shape and mechanical stability, and is essential for sporozoite infectivity in insect and vertebrate hosts. Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion. We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites. These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

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Sporozoite gliding motility and resistance to osmotic shock. (A) Circular gliding of sporozoites on glass slides. Frames are taken at 10-s intervals. (B) Swelling of sporozoites exposed to 0.33× normal osmotic strength, compared with untreated cells (1.0×). Nuclei are stained with DAPI (blue). (C) Percent sporozoite survival/death after hypo-osmotic shock (5-min exposure to 0.33× normal osmotic strength, values normalized to 100% viability in untreated cells). Error bars indicate SDs from two independent experiments. At least 100 cells were scored for each sample. WT: wild-type, KO: PbIMC1a-KO.
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fig5: Sporozoite gliding motility and resistance to osmotic shock. (A) Circular gliding of sporozoites on glass slides. Frames are taken at 10-s intervals. (B) Swelling of sporozoites exposed to 0.33× normal osmotic strength, compared with untreated cells (1.0×). Nuclei are stained with DAPI (blue). (C) Percent sporozoite survival/death after hypo-osmotic shock (5-min exposure to 0.33× normal osmotic strength, values normalized to 100% viability in untreated cells). Error bars indicate SDs from two independent experiments. At least 100 cells were scored for each sample. WT: wild-type, KO: PbIMC1a-KO.

Mentions: Gliding locomotion is necessary for cell invasion in sporozoites (Sultan et al., 1997). Therefore, we examined the ability of the sporozoites to glide in vitro. Observing live gliding of oocyst sporozoites on glass slides clearly showed that locomotion was compromised by the PbIMC1a knockout: mutant sporozoites were able to attach normally to the glass surface and undergo circular gliding, but their gliding speed was fivefold slower than that of WT sporozoites (WT 2.5 ± 0.4 circles min−1; PbIMC1a-KO 0.5 ± 0.1 circles min−1; n = 7) (Fig. 5 A). Possibly as a consequence of the reduced speed, the percentage of attached PbIMC1a-KO sporozoites observed to be gliding within a set time frame was just half that of WT sporozoites (WT 32%; PbIMC1a-KO 17%; n = 53). These results indicate that PbIMC1a is not a vital component of the motility machinery of the cell, which is closely associated with the pellicle structure (for review see Kappe et al., 2004). Possibly, the reduced motility of the knockout sporozoites is an effect of their abnormal cell shape or size. Alternately, PbIMC1a may interact directly or indirectly with components of the gliding machinery. The molecular interactions involved in gliding are known to be complex and involve multiple protein components besides actin and myosin, such as myosin A tail domain-interacting protein (Bergman et al., 2002), aldolase (Buscaglia et al., 2003; Jewett and Sibley, 2003), and membrane receptors (Gaskins et al., 2004). Given the opportunities for multiple protein interactions, as well as the existence of multiple PbIMC1a homologues, some functional redundancy may exist, resulting in reduced rather than abolished motility. Given the essential connection between gliding motility and cell invasion, the reduced motility of PbIMC1a-KO sporozoites could be partly or solely responsible for their lack of infectivity.


A malaria membrane skeletal protein is essential for normal morphogenesis, motility, and infectivity of sporozoites.

Khater EI, Sinden RE, Dessens JT - J. Cell Biol. (2004)

Sporozoite gliding motility and resistance to osmotic shock. (A) Circular gliding of sporozoites on glass slides. Frames are taken at 10-s intervals. (B) Swelling of sporozoites exposed to 0.33× normal osmotic strength, compared with untreated cells (1.0×). Nuclei are stained with DAPI (blue). (C) Percent sporozoite survival/death after hypo-osmotic shock (5-min exposure to 0.33× normal osmotic strength, values normalized to 100% viability in untreated cells). Error bars indicate SDs from two independent experiments. At least 100 cells were scored for each sample. WT: wild-type, KO: PbIMC1a-KO.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172497&req=5

fig5: Sporozoite gliding motility and resistance to osmotic shock. (A) Circular gliding of sporozoites on glass slides. Frames are taken at 10-s intervals. (B) Swelling of sporozoites exposed to 0.33× normal osmotic strength, compared with untreated cells (1.0×). Nuclei are stained with DAPI (blue). (C) Percent sporozoite survival/death after hypo-osmotic shock (5-min exposure to 0.33× normal osmotic strength, values normalized to 100% viability in untreated cells). Error bars indicate SDs from two independent experiments. At least 100 cells were scored for each sample. WT: wild-type, KO: PbIMC1a-KO.
Mentions: Gliding locomotion is necessary for cell invasion in sporozoites (Sultan et al., 1997). Therefore, we examined the ability of the sporozoites to glide in vitro. Observing live gliding of oocyst sporozoites on glass slides clearly showed that locomotion was compromised by the PbIMC1a knockout: mutant sporozoites were able to attach normally to the glass surface and undergo circular gliding, but their gliding speed was fivefold slower than that of WT sporozoites (WT 2.5 ± 0.4 circles min−1; PbIMC1a-KO 0.5 ± 0.1 circles min−1; n = 7) (Fig. 5 A). Possibly as a consequence of the reduced speed, the percentage of attached PbIMC1a-KO sporozoites observed to be gliding within a set time frame was just half that of WT sporozoites (WT 32%; PbIMC1a-KO 17%; n = 53). These results indicate that PbIMC1a is not a vital component of the motility machinery of the cell, which is closely associated with the pellicle structure (for review see Kappe et al., 2004). Possibly, the reduced motility of the knockout sporozoites is an effect of their abnormal cell shape or size. Alternately, PbIMC1a may interact directly or indirectly with components of the gliding machinery. The molecular interactions involved in gliding are known to be complex and involve multiple protein components besides actin and myosin, such as myosin A tail domain-interacting protein (Bergman et al., 2002), aldolase (Buscaglia et al., 2003; Jewett and Sibley, 2003), and membrane receptors (Gaskins et al., 2004). Given the opportunities for multiple protein interactions, as well as the existence of multiple PbIMC1a homologues, some functional redundancy may exist, resulting in reduced rather than abolished motility. Given the essential connection between gliding motility and cell invasion, the reduced motility of PbIMC1a-KO sporozoites could be partly or solely responsible for their lack of infectivity.

Bottom Line: Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion.We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites.These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Imperail College London, London SW7 2AZ, England, UK.

ABSTRACT
Membrane skeletons are structural elements that provide mechanical support to the plasma membrane and define cell shape. Here, we identify and characterize a putative protein component of the membrane skeleton of the malaria parasite. The protein, named PbIMC1a, is the structural orthologue of the Toxoplasma gondii inner membrane complex protein 1 (TgIMC1), a component of the membrane skeleton in tachyzoites. Using targeted gene disruption in the rodent malaria species Plasmodium berghei, we show that PbIMC1a is involved in sporozoite development, is necessary for providing normal sporozoite cell shape and mechanical stability, and is essential for sporozoite infectivity in insect and vertebrate hosts. Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion. We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites. These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.

Show MeSH
Related in: MedlinePlus