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Trafficking of plasmepsin II to the food vacuole of the malaria parasite Plasmodium falciparum.

Klemba M, Beatty W, Gluzman I, Goldberg DE - J. Cell Biol. (2004)

Bottom Line: A family of aspartic proteases, the plasmepsins (PMs), plays a key role in the degradation of hemoglobin in the Plasmodium falciparum food vacuole.To study the trafficking of proPM II, we have modified the chromosomal PM II gene in P. falciparum to encode a proPM II-GFP chimera.Our data support a model whereby proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Ave., Box 8230, St. Louis, MO 63110, USA.

ABSTRACT
A family of aspartic proteases, the plasmepsins (PMs), plays a key role in the degradation of hemoglobin in the Plasmodium falciparum food vacuole. To study the trafficking of proPM II, we have modified the chromosomal PM II gene in P. falciparum to encode a proPM II-GFP chimera. By taking advantage of green fluorescent protein fluorescence in live parasites, the ultrastructural resolution of immunoelectron microscopy, and inhibitors of trafficking and PM maturation, we have investigated the biosynthetic path leading to mature PM II in the food vacuole. Our data support a model whereby proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II.

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Model for trafficking of proPM II–GFP to the food vacuole. This model is based on data presented here and elsewhere (Francis et al., 1994, 1997a). proPM II–GFP is inserted as a type II membrane protein into the ER/nuclear envelope (NE). Transport vesicles containing proPM II–GFP bud from ER exit sites in a BFA-sensitive manner. The vesicles migrate to the cytostome (possibly via a Golgi-like compartment) and fuse with the outer membrane of the cytostomal vacuole, which is topologically contiguous with the parasite plasma membrane. This event would place proPM II–GFP in the space between the two vacuole membranes. The double-membrane hemoglobin transport vesicle pinches off from the cytostome, migrates to the food vacuole, and its outer membrane fuses with that of the food vacuole, leaving proPM II–GFP anchored in the food vacuole membrane. The proregion of PM II and GFP are proteolytically removed to yield mPM II, a process that is inhibited by ALLN. Black circles, PM II; white circles, GFP; PVM, parasitophorous vacuole membrane; PPM, parasite plasma membrane; Hb, hemoglobin.
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fig8: Model for trafficking of proPM II–GFP to the food vacuole. This model is based on data presented here and elsewhere (Francis et al., 1994, 1997a). proPM II–GFP is inserted as a type II membrane protein into the ER/nuclear envelope (NE). Transport vesicles containing proPM II–GFP bud from ER exit sites in a BFA-sensitive manner. The vesicles migrate to the cytostome (possibly via a Golgi-like compartment) and fuse with the outer membrane of the cytostomal vacuole, which is topologically contiguous with the parasite plasma membrane. This event would place proPM II–GFP in the space between the two vacuole membranes. The double-membrane hemoglobin transport vesicle pinches off from the cytostome, migrates to the food vacuole, and its outer membrane fuses with that of the food vacuole, leaving proPM II–GFP anchored in the food vacuole membrane. The proregion of PM II and GFP are proteolytically removed to yield mPM II, a process that is inhibited by ALLN. Black circles, PM II; white circles, GFP; PVM, parasitophorous vacuole membrane; PPM, parasite plasma membrane; Hb, hemoglobin.

Mentions: Together, these results suggest a trafficking pathway for proPM II that takes advantage of the parasite's nutritional requirement for hemoglobin degradation (Fig. 8). We propose that, after insertion into the ER, proPM II is transported to the cytostome, where it accumulates and is brought to the food vacuole along with its substrate, hemoglobin. In the acidic environment of the food vacuole, the proenzyme is cleaved and mature, active, soluble PM II is released. The half-time for biosynthesis and maturation of untagged PMs has been estimated to be 20 min (Francis et al., 1997a; Banerjee et al., 2003). If PM II is trafficked exclusively through the cytostome, we can estimate that the half-time for the delivery of cytostomal vacuolar contents to the food vacuole is less than 20 min; however, our data do not exclude the possibility of alternate PM II trafficking pathways such as direct transport from the ER to the food vacuole.


Trafficking of plasmepsin II to the food vacuole of the malaria parasite Plasmodium falciparum.

Klemba M, Beatty W, Gluzman I, Goldberg DE - J. Cell Biol. (2004)

Model for trafficking of proPM II–GFP to the food vacuole. This model is based on data presented here and elsewhere (Francis et al., 1994, 1997a). proPM II–GFP is inserted as a type II membrane protein into the ER/nuclear envelope (NE). Transport vesicles containing proPM II–GFP bud from ER exit sites in a BFA-sensitive manner. The vesicles migrate to the cytostome (possibly via a Golgi-like compartment) and fuse with the outer membrane of the cytostomal vacuole, which is topologically contiguous with the parasite plasma membrane. This event would place proPM II–GFP in the space between the two vacuole membranes. The double-membrane hemoglobin transport vesicle pinches off from the cytostome, migrates to the food vacuole, and its outer membrane fuses with that of the food vacuole, leaving proPM II–GFP anchored in the food vacuole membrane. The proregion of PM II and GFP are proteolytically removed to yield mPM II, a process that is inhibited by ALLN. Black circles, PM II; white circles, GFP; PVM, parasitophorous vacuole membrane; PPM, parasite plasma membrane; Hb, hemoglobin.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171955&req=5

fig8: Model for trafficking of proPM II–GFP to the food vacuole. This model is based on data presented here and elsewhere (Francis et al., 1994, 1997a). proPM II–GFP is inserted as a type II membrane protein into the ER/nuclear envelope (NE). Transport vesicles containing proPM II–GFP bud from ER exit sites in a BFA-sensitive manner. The vesicles migrate to the cytostome (possibly via a Golgi-like compartment) and fuse with the outer membrane of the cytostomal vacuole, which is topologically contiguous with the parasite plasma membrane. This event would place proPM II–GFP in the space between the two vacuole membranes. The double-membrane hemoglobin transport vesicle pinches off from the cytostome, migrates to the food vacuole, and its outer membrane fuses with that of the food vacuole, leaving proPM II–GFP anchored in the food vacuole membrane. The proregion of PM II and GFP are proteolytically removed to yield mPM II, a process that is inhibited by ALLN. Black circles, PM II; white circles, GFP; PVM, parasitophorous vacuole membrane; PPM, parasite plasma membrane; Hb, hemoglobin.
Mentions: Together, these results suggest a trafficking pathway for proPM II that takes advantage of the parasite's nutritional requirement for hemoglobin degradation (Fig. 8). We propose that, after insertion into the ER, proPM II is transported to the cytostome, where it accumulates and is brought to the food vacuole along with its substrate, hemoglobin. In the acidic environment of the food vacuole, the proenzyme is cleaved and mature, active, soluble PM II is released. The half-time for biosynthesis and maturation of untagged PMs has been estimated to be 20 min (Francis et al., 1997a; Banerjee et al., 2003). If PM II is trafficked exclusively through the cytostome, we can estimate that the half-time for the delivery of cytostomal vacuolar contents to the food vacuole is less than 20 min; however, our data do not exclude the possibility of alternate PM II trafficking pathways such as direct transport from the ER to the food vacuole.

Bottom Line: A family of aspartic proteases, the plasmepsins (PMs), plays a key role in the degradation of hemoglobin in the Plasmodium falciparum food vacuole.To study the trafficking of proPM II, we have modified the chromosomal PM II gene in P. falciparum to encode a proPM II-GFP chimera.Our data support a model whereby proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Ave., Box 8230, St. Louis, MO 63110, USA.

ABSTRACT
A family of aspartic proteases, the plasmepsins (PMs), plays a key role in the degradation of hemoglobin in the Plasmodium falciparum food vacuole. To study the trafficking of proPM II, we have modified the chromosomal PM II gene in P. falciparum to encode a proPM II-GFP chimera. By taking advantage of green fluorescent protein fluorescence in live parasites, the ultrastructural resolution of immunoelectron microscopy, and inhibitors of trafficking and PM maturation, we have investigated the biosynthetic path leading to mature PM II in the food vacuole. Our data support a model whereby proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II.

Show MeSH
Related in: MedlinePlus