Haemoproteus and Schistosoma synthesize heme polymers similar to Plasmodium hemozoin and beta-hematin

Abstract

Many parasites digest hemoglobin as an amino acid source, but only a few produce heme polymer pigment instead of catabolizing heme via heme oxygenase. This work compares purified heme polymers produced by Haemoproteus columbae and Schistosoma mansoni to that of Plasmodium falciparum hemozoin and synthetic beta-hematin. Fourier-transform infrared spectroscopy identifies the signature peaks of the common iron-carboxylate bond characteristic in all four heme polymers. However, all pigments could be distinguished by quite different three-dimensional structure visualized by Field Emission Inlens Scanning Electron Microscopy. Both P. falciparum and H. columbae heme polymers had a symmetrical shape unlike the amorphous S. mansoni heme polymer and beta-hematin. All four heme pigments serve as templates for heme polymer extension, which was inhibitable by chloroquine and other quinoline antimalarials. The polymers showed different levels of resistance to hydrogen peroxide degradation. This work identifies another genus, Haemoproteus, capable of intracellular heme polymer formation. The different three-dimensional structures of each pigment implicate genus specific formation of heme polymer, variation of inhibition of polymer extension by the quinolines and degradation by hydrogen peroxide.