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IMC1b is a putative membrane skeleton protein involved in cell shape, mechanical strength, motility, and infectivity of malaria ookinetes.

Tremp AZ, Khater EI, Dessens JT - J. Biol. Chem. (2008)

Bottom Line: We also show that IMC1b-deficient ookinetes display abnormal cell shape, reduced gliding motility, decreased mechanical strength, and reduced infectivity.The similarities observed between the loss-of-function phenotypes of IMC1a and IMC1b show that membrane skeletons of ookinetes and sporozoites function in an overall similar way.However, the fact that ookinetes and sporozoites do not use the same IMC1 protein implies that different mechanical properties are required of their respective membrane skeletons, likely reflecting the distinct environments in which these life stages must operate.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom.

ABSTRACT
Membrane skeletons are cytoskeletal elements that have important roles in cell development, shape, and structural integrity. Malaria parasites encode a conserved family of putative membrane skeleton proteins related to articulins. One member, IMC1a, is expressed in sporozoites and localizes to the pellicle, a unique membrane complex believed to form a scaffold onto which the ligands and glideosome are arranged to mediate parasite motility and invasion. IMC1b is a closely related structural paralogue of IMC1a, fostering speculation that it could be functionally homologous but in a different invasive life stage. Here we have generated genetically modified parasites that express IMC1b tagged with green fluorescent protein, and we show that it is targeted exclusively to the pellicle of ookinetes. We also show that IMC1b-deficient ookinetes display abnormal cell shape, reduced gliding motility, decreased mechanical strength, and reduced infectivity. These findings are consistent with a membrane skeletal role of IMC1b and provide strong experimental support for the view that membrane skeletons form an integral part of the pellicle of apicomplexan zoites and function to provide rigidity to the pellicular membrane complex. The similarities observed between the loss-of-function phenotypes of IMC1a and IMC1b show that membrane skeletons of ookinetes and sporozoites function in an overall similar way. However, the fact that ookinetes and sporozoites do not use the same IMC1 protein implies that different mechanical properties are required of their respective membrane skeletons, likely reflecting the distinct environments in which these life stages must operate.

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Sequence and structure of Plasmodium IMC1b. A, multiple amino acid sequence alignment of the predicted IMC1b proteins from P. berghei (Pb), P. yoelii (Py), P. chabaudi (Pc), P. knowlesi (Pk), P. vivax (Pv), P. falciparum (Pf), and P. gallinaceum (Pg). Indicated are three conserved domains (shaded), and gaps were introduced to allow optimal alignment (hyphens). Conserved amino acid identities (asterisks) and similarities (colons and points) are indicated below. The alignment was made with ClustalW with default parameters. B, schematic diagram of the protein structures of TgIMC1 and its structural relatives PxIMC1a and PxIMC1b in Plasmodium. Boxes mark domains corresponding to the amino-terminal (hatched), central (gray), and carboxyl-terminal (open) conserved domains highlighted in A. Conserved terminal cysteine motifs are indicated by open circles.
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fig1: Sequence and structure of Plasmodium IMC1b. A, multiple amino acid sequence alignment of the predicted IMC1b proteins from P. berghei (Pb), P. yoelii (Py), P. chabaudi (Pc), P. knowlesi (Pk), P. vivax (Pv), P. falciparum (Pf), and P. gallinaceum (Pg). Indicated are three conserved domains (shaded), and gaps were introduced to allow optimal alignment (hyphens). Conserved amino acid identities (asterisks) and similarities (colons and points) are indicated below. The alignment was made with ClustalW with default parameters. B, schematic diagram of the protein structures of TgIMC1 and its structural relatives PxIMC1a and PxIMC1b in Plasmodium. Boxes mark domains corresponding to the amino-terminal (hatched), central (gray), and carboxyl-terminal (open) conserved domains highlighted in A. Conserved terminal cysteine motifs are indicated by open circles.

Mentions: IMC1b Sequence and Structure—Among the paralogues of Plasmodium IMC1a, IMC1b is structurally the most closely related as it shares three conserved domains with IMC1a (5). The P. berghei IMC1b gene was identified from BLAST searches of P. berghei genomic sequences with the IMC1b sequence from Plasmodium yoelii (GenBank™/EMBL/DDJB accession number EAA15257). Three overlapping sequences were identified (PB_RP1359, berg-2278d04.qlk, and PB_RP2104) from which the entire P. berghei IMC1b coding sequence could be assembled. IMC1b is encoded by a single exon. The predicted full-length protein is composed of 535 amino acids with a predicted Mr of 62,590 sharing 93% amino acid sequence identity with its orthologue in P. yoelii. BLAST searches identified orthologues in all other Plasmodium species examined, including Plasmodium falciparum (AAN36013), Plasmodium vivax (EDL45805), Plasmodium chabaudi (CAH84924), Plasmodium knowlesi (PKH_093930), and Plasmodium gallinaceum (gal28a.d000013616.Contig1). A multiple alignment of the IMC1b orthologues reveals the presence of three conserved domains, separated by regions of variable length and sequence (Fig. 1A). These three domains, the first two of which are structurally related to articulins, are conserved in the T. gondii membrane skeleton protein TgIMC1 as well as in IMC1a (Fig. 1B) (4, 5). None of the Plasmodium IMC1b proteins identified possess the cysteine motifs at amino and carboxyl termini described in TgIMC1 and PbIMC1a (Fig. 1B) (5, 15).


IMC1b is a putative membrane skeleton protein involved in cell shape, mechanical strength, motility, and infectivity of malaria ookinetes.

Tremp AZ, Khater EI, Dessens JT - J. Biol. Chem. (2008)

Sequence and structure of Plasmodium IMC1b. A, multiple amino acid sequence alignment of the predicted IMC1b proteins from P. berghei (Pb), P. yoelii (Py), P. chabaudi (Pc), P. knowlesi (Pk), P. vivax (Pv), P. falciparum (Pf), and P. gallinaceum (Pg). Indicated are three conserved domains (shaded), and gaps were introduced to allow optimal alignment (hyphens). Conserved amino acid identities (asterisks) and similarities (colons and points) are indicated below. The alignment was made with ClustalW with default parameters. B, schematic diagram of the protein structures of TgIMC1 and its structural relatives PxIMC1a and PxIMC1b in Plasmodium. Boxes mark domains corresponding to the amino-terminal (hatched), central (gray), and carboxyl-terminal (open) conserved domains highlighted in A. Conserved terminal cysteine motifs are indicated by open circles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC2562075&req=5

fig1: Sequence and structure of Plasmodium IMC1b. A, multiple amino acid sequence alignment of the predicted IMC1b proteins from P. berghei (Pb), P. yoelii (Py), P. chabaudi (Pc), P. knowlesi (Pk), P. vivax (Pv), P. falciparum (Pf), and P. gallinaceum (Pg). Indicated are three conserved domains (shaded), and gaps were introduced to allow optimal alignment (hyphens). Conserved amino acid identities (asterisks) and similarities (colons and points) are indicated below. The alignment was made with ClustalW with default parameters. B, schematic diagram of the protein structures of TgIMC1 and its structural relatives PxIMC1a and PxIMC1b in Plasmodium. Boxes mark domains corresponding to the amino-terminal (hatched), central (gray), and carboxyl-terminal (open) conserved domains highlighted in A. Conserved terminal cysteine motifs are indicated by open circles.
Mentions: IMC1b Sequence and Structure—Among the paralogues of Plasmodium IMC1a, IMC1b is structurally the most closely related as it shares three conserved domains with IMC1a (5). The P. berghei IMC1b gene was identified from BLAST searches of P. berghei genomic sequences with the IMC1b sequence from Plasmodium yoelii (GenBank™/EMBL/DDJB accession number EAA15257). Three overlapping sequences were identified (PB_RP1359, berg-2278d04.qlk, and PB_RP2104) from which the entire P. berghei IMC1b coding sequence could be assembled. IMC1b is encoded by a single exon. The predicted full-length protein is composed of 535 amino acids with a predicted Mr of 62,590 sharing 93% amino acid sequence identity with its orthologue in P. yoelii. BLAST searches identified orthologues in all other Plasmodium species examined, including Plasmodium falciparum (AAN36013), Plasmodium vivax (EDL45805), Plasmodium chabaudi (CAH84924), Plasmodium knowlesi (PKH_093930), and Plasmodium gallinaceum (gal28a.d000013616.Contig1). A multiple alignment of the IMC1b orthologues reveals the presence of three conserved domains, separated by regions of variable length and sequence (Fig. 1A). These three domains, the first two of which are structurally related to articulins, are conserved in the T. gondii membrane skeleton protein TgIMC1 as well as in IMC1a (Fig. 1B) (4, 5). None of the Plasmodium IMC1b proteins identified possess the cysteine motifs at amino and carboxyl termini described in TgIMC1 and PbIMC1a (Fig. 1B) (5, 15).

Bottom Line: We also show that IMC1b-deficient ookinetes display abnormal cell shape, reduced gliding motility, decreased mechanical strength, and reduced infectivity.The similarities observed between the loss-of-function phenotypes of IMC1a and IMC1b show that membrane skeletons of ookinetes and sporozoites function in an overall similar way.However, the fact that ookinetes and sporozoites do not use the same IMC1 protein implies that different mechanical properties are required of their respective membrane skeletons, likely reflecting the distinct environments in which these life stages must operate.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom.

ABSTRACT
Membrane skeletons are cytoskeletal elements that have important roles in cell development, shape, and structural integrity. Malaria parasites encode a conserved family of putative membrane skeleton proteins related to articulins. One member, IMC1a, is expressed in sporozoites and localizes to the pellicle, a unique membrane complex believed to form a scaffold onto which the ligands and glideosome are arranged to mediate parasite motility and invasion. IMC1b is a closely related structural paralogue of IMC1a, fostering speculation that it could be functionally homologous but in a different invasive life stage. Here we have generated genetically modified parasites that express IMC1b tagged with green fluorescent protein, and we show that it is targeted exclusively to the pellicle of ookinetes. We also show that IMC1b-deficient ookinetes display abnormal cell shape, reduced gliding motility, decreased mechanical strength, and reduced infectivity. These findings are consistent with a membrane skeletal role of IMC1b and provide strong experimental support for the view that membrane skeletons form an integral part of the pellicle of apicomplexan zoites and function to provide rigidity to the pellicular membrane complex. The similarities observed between the loss-of-function phenotypes of IMC1a and IMC1b show that membrane skeletons of ookinetes and sporozoites function in an overall similar way. However, the fact that ookinetes and sporozoites do not use the same IMC1 protein implies that different mechanical properties are required of their respective membrane skeletons, likely reflecting the distinct environments in which these life stages must operate.

Show MeSH
Related in: MedlinePlus