A lipocalin mediates unidirectional haem biomineralization in malaria parasites

Abstract

18During blood stage development, malaria parasites are challenged with the detoxification of 19 enormous amounts of haem released during the proteolytic catabolism of erythrocytic 20 haemoglobin. They tackle this problem by sequestering haem into bioinert crystals known as 21 haemozoin. The mechanisms underlying this biomineralization process remain enigmatic. 22Here, we demonstrate that both rodent and human malaria parasite species secrete and 23 internalize a lipocalin-like protein, PV5, to control haem crystallization. Transcriptional 24 deregulation of PV5 in the rodent parasite Plasmodium berghei results in inordinate elongation 25 of haemozoin crystals, while conditional PV5 inactivation in the human malaria agent 26 Plasmodium falciparum causes excessive multi-directional crystal branching. Although 27 haemoglobin processing remains unaffected, PV5-deficient parasites generate less 28 haemozoin. Electron diffraction analysis indicates that despite the distinct changes in crystal 29 morphology neither the crystalline order nor unit cell of haemozoin are affected by impaired 30 PV5 function. Deregulation of PV5 expression renders P. berghei hypersensitive to the 31 antimalarial drugs artesunate, chloroquine, and atovaquone, resulting in accelerated parasite 32 clearance following drug treatment in vivo. Together, our findings demonstrate the 33 Plasmodium-tailored role of a lipocalin family member in haemozoin formation and underscore 34 the haem biomineralization pathway as an attractive target for therapeutic exploitation.35 SIGNIFICANCE 37During blood stage development, the malaria parasite replicates inside erythrocytes of the 38 vertebrate host, where it engulfs and digests most of the available haemoglobin. This results 39 in release of the oxygen-binding prosthetic group haem, which is highly toxic in its unbound 40 form. The parasite crystallizes the haem into an insoluble pigment called haemozoin, a 41 process that is vital for parasite survival and which is exploited in antimalarial therapy. We 42 demonstrate that the parasite uses a protein called PV5 in haemozoin formation and that 43 interfering with PV5 expression can increase the parasite's sensitivity to antimalarial drugs 44 during blood infection. An improved understanding of the mechanisms underlying haem 45 sequestration will provide valuable insights for future drug development efforts.(1). Throughout blood stage development, the parasite ingests and catabolizes up to 80% of 50 the host cell cytoplasm, facilitating amino acid acquisition and making sufficient room for 51 parasite growth (2, 3). Haemoglobin is incorporated through endocytosis and then degraded 52 by an array of functionally redundant proteases, a process which occurs in acidified lysosome-53 like organelles with species-specific morphology (4). In the rodent-infective parasite species 54 Plasmodium berghei, one or more food vacuoles (FVs) give rise to small digestive vesicles 55 (DVs) which only fuse at the very end of intraerythrocytic development (5). By contrast, the...

Cryo-tomography and 3D Electron Diffraction Reveal the Polar Habit and Chiral Structure of the Malaria Pigment Crystal Hemozoin

“…For example, knockout of a lipocalin-family protein leads to strongly branched growth of hemozoin in P. falciparum, but instead to twinned growth in P. berghei. 22,60 Hemozoin forms as well in a number of other blood-feeding organisms, including the blood fluke Schistosoma mansoni and the kissing bug Rhodnius prolixus. In contrast to Plasmodium, in these cases the crystal growth environment is extracellular.…”

COVID-19:Attacks the 1-Beta Chain of Hemoglobin and Captures the Porphyrin to Inhibit Human Heme Metabolism

“…Heme is isolated from the host hemoglobin and kept as heme crystals to prevent poisoning by free heme (56). Heme is initially oxidized to yield hematin, which then dimerizes through the reciprocal coordination of iron and propionate moieties (57). Heme is a very hazardous byproduct of hemoglobin metabolism (58).…”

“…With the assistance of detoxification protein, it is transformed into crystal heme (58). This molecular unit then assembles into Hz crystals that typically take the form of triclinic high aspect ratio parallelograms (57). Chloroquine, a conjugated antimalarial medication, inhibits heme crystallization, increasing unstable heme (59).…”

Revealing Chloroquine’s Antimalarial Mechanism: The Suppression of Nucleation Events during Heme to Hemozoin Transformation

“…Generally, these theories either support spontaneous transformation [12]- [13], lipid-mediated [14][15] [16], or protein-mediated conversion of heme into Hz [17] [18][19] [20] [21]. Among all known mediators of Hz production, heme detoxification protein (HDP; UniProt ID: Q8IL04) is shown to be most efficient under in-vitro settings and proven indispensable for the parasite's viability [19].…”