Quantification of labile heme in live malaria parasites using a genetically encoded biosensor
Malaria parasites degrade substantial quantities of hemoglobin to release heme within a specialized digestive vacuole. Most of this heme is sequestered in an inert crystal. However, the concentration of bioavailable, labile heme in the parasite’s cytosol was unknown. We developed a biosensor to provide the first quantitative insights into labile heme concentrations in malaria parasites. We find that ∼1.6 µM labile cytosolic heme is maintained, including during a period coincident with intense hemoglobin degradation. The heme-binding antimalarial drug, chloroquine, which interferes with heme crystallization, specifically induces an increase in labile heme. The ability to quantify labile heme in malaria parasites opens opportunities for better understanding heme homeostasis, signaling, and metabolism, and its association with antimalarial potency.