Abstract
PfEMP1 (erythrocyte membrane protein 1) adhesins play a pivotal role in the pathophysiology of falciparum malaria, by mediating sequestration of Plasmodium falciparum-infected erythrocytes in the microvasculature. PfEMP1 variants are expressed by var genes and are presented on membrane elevations, termed knobs. However, the organization of PfEMP1 on knobs is largely unclear. Here, we use super-resolution microscopy and genetically altered parasites expressing a modified var2csa gene in which the coding sequence of the photoactivatable mEOS2 was inserted to determine the number and distribution of PfEMP1 on single knobs. The data were verified by quantitative fluorescence-activated cell sorting analysis and immuno-electron microscopy together with stereology methods. We show that knobs contain 3.3 ± 1.7 and 4.3 ± 2.5 PfEMP1 molecules, predominantly placed on the knob tip, in parasitized erythrocytes containing wild type and sickle haemoglobin, respectively. The ramifications of our findings for cytoadhesion and immune evasion are discussed.
Highlights
PfEMP1 adhesins play a pivotal role in the pathophysiology of falciparum malaria, by mediating sequestration of Plasmodium falciparum-infected erythrocytes in the microvasculature
Our data show that knobs contain an unexpected low number of VAR2CSA molecules (3.3 ± 1.7 and 4.3 ± 2.5 molecules per knob in parasitized erythrocytes containing wild type and sickle haemoglobin, respectively) that are predominantly placed at the tip of the knob
Attempts to insert the tag into the DBL6ε domain failed, resulting in a chromosome truncation event in which the end of chromosome 12 including most of the ectodomain-encoding sequence of var2csa was deleted
Summary
PfEMP1 (erythrocyte membrane protein 1) adhesins play a pivotal role in the pathophysiology of falciparum malaria, by mediating sequestration of Plasmodium falciparum-infected erythrocytes in the microvasculature. Enlarged and widely dispersed knobs are associated with a reduced capacity of parasitized haemoglobinopathic erythrocytes to engage in cytoadhesive interactions, and are thought to contribute to the malaria-protective function of sickle cell haemoglobin and related haemoglobinopathies[17,18,21,22] This dearth of information has been partly owing to a shortage of enabling technology to visualize single PfEMP1 molecules. We have used photoactivated light microscopy (PALM) of genetically engineered parasites expressing a modified var2csa gene in which the coding sequence of two copies of mEOS2 was inserted to study the numerical and spatial organization of PfEMP1 molecules on single knobs in infected erythrocyte containing wild type or sickle cell haemoglobin. Mathematical simulations suggest that this spatial organization has evolved to evade antibody-mediated immune effector mechanisms and increase the capture radius of single VAR2CSA molecules and, receptor binding
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
