Characterization of Host Cell Cytosol-filled Vesicles in the Human Malaria Parasite Plasmodium falciparum
- 1Bernhard Nocht Institute for Tropical Medicine
Abstract
Endocytosis of host cell cytosol is a key process in malaria blood stages. The endocytosed material consists mostly of haemoglobin (Hb) and is transported to the parasite's digestive vacuole (DV), where it is degraded. However, the endosomal transport pathway of the parasite is not well defined. A number of proteins are known that - when inactivated - lead to the appearance of Hb-filled vesicles (HbVs) in the parasite cytoplasm and prevent Hb from arriving in the DV, indicating they play a role in endosomal transport. However, despite the prominence of these HbVs, their morphology, molecular composition, and relationship to the endosomal transport pathway remain poorly understood. Here we carried out a morphological and surface proteome study of HbVs. CryoET showed HbVs are coatless, double membraned vesicles with a very narrow inter-membrane space devoid of larger protein densities. HbV surface proteomes generated by BioIDs most prominently detected DV proteases. Halo-based tracking of one of these DV protease confirmed it as a bona fide HbV cargo. The BioID also identified a number of vesicle trafficking proteins, including PfTBC8 and Rab11 proteins. Functional analysis of PfTBC8 showed its importance for the transport of Hb to the DV. This was due to a novel phenotype characterized by accumulation of diverse Hb-filled structures in the parasite cytosol and gradual decline of DV protease trafficking. PfTBC8 DiQ-BioID detected Rab11a and PfTBC8 inactivation altered Rab11a localization, suggesting it may be a Rab11a effector and that the new endosomal transport phenotype may result from a recycling defect. Together with the detection of VPS35 in the BioID and evidence from the CryoET of a disrupted inner HbV membrane in a proportion of vesicles, these findings support a model in which HbVs undergo maturation prior to fusion with the DV. Overall, our findings define morphological and molecular features of HbVs, identify protein cargo transported through this pathway, and reveal a previously unrecognized Rab-regulatory component required for endosomal trafficking in blood-stage P. falciparum parasites.
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BibTeX
@misc{rossmann2026characterization,
title = {{Characterization of Host Cell Cytosol-filled Vesicles in the Human Malaria Parasite Plasmodium falciparum}},
author = {A.-L. Rossmann and J. Droege and H. Wang and C. Duda and J. Zhen and R. Sabitzki and K. Hoehn and G. B. Farias and A. Guillen Samander and T. Gilberger and C.-M. Ho and T. Spielmann},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.10.750675},
url = {https://www.biorxiv.org/content/10.64898/2026.09.10.750675v1},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - Characterization of Host Cell Cytosol-filled Vesicles in the Human Malaria Parasite Plasmodium falciparum
AU - A.-L. Rossmann
AU - J. Droege
AU - H. Wang
AU - C. Duda
AU - J. Zhen
AU - R. Sabitzki
AU - K. Hoehn
AU - G. B. Farias
AU - A. Guillen Samander
AU - T. Gilberger
AU - C.-M. Ho
AU - T. Spielmann
PY - 2026
DA - 2026/09/10
PB - bioRxiv
DO - 10.64898/2026.09.10.750675
UR - https://www.biorxiv.org/content/10.64898/2026.09.10.750675v1
AB - Endocytosis of host cell cytosol is a key process in malaria blood stages. The endocytosed material consists mostly of haemoglobin (Hb) and is transported to the parasite's digestive vacuole (DV), where it is degraded. However, the endosomal transport pathway of the parasite is not well defined. A number of proteins are known that - when inactivated - lead to the appearance of Hb-filled vesicles (HbVs) in the parasite cytoplasm and prevent Hb from arriving in the DV, indicating they play a role in endosomal transport. However, despite the prominence of these HbVs, their morphology, molecular composition, and relationship to the endosomal transport pathway remain poorly understood. Here we carried out a morphological and surface proteome study of HbVs. CryoET showed HbVs are coatless, double membraned vesicles with a very narrow inter-membrane space devoid of larger protein densities. HbV surface proteomes generated by BioIDs most prominently detected DV proteases. Halo-based tracking of one of these DV protease confirmed it as a bona fide HbV cargo. The BioID also identified a number of vesicle trafficking proteins, including PfTBC8 and Rab11 proteins. Functional analysis of PfTBC8 showed its importance for the transport of Hb to the DV. This was due to a novel phenotype characterized by accumulation of diverse Hb-filled structures in the parasite cytosol and gradual decline of DV protease trafficking. PfTBC8 DiQ-BioID detected Rab11a and PfTBC8 inactivation altered Rab11a localization, suggesting it may be a Rab11a effector and that the new endosomal transport phenotype may result from a recycling defect. Together with the detection of VPS35 in the BioID and evidence from the CryoET of a disrupted inner HbV membrane in a proportion of vesicles, these findings support a model in which HbVs undergo maturation prior to fusion with the DV. Overall, our findings define morphological and molecular features of HbVs, identify protein cargo transported through this pathway, and reveal a previously unrecognized Rab-regulatory component required for endosomal trafficking in blood-stage P. falciparum parasites.
ER -