Characterization of the Products of the Heme Detoxification Pathway in Malarial Late Trophozoites by X-ray Diffraction
Heme is a potent multifunction regulator whose biochemical levels and distribution are precisely controlled on both intra- and extracellular levels. Efficient regulation of heme is particularly critical for intra-erythrocytic parasites such as plasmodia which process large quantities of heme in the post-invasion digestion of the erythrocyte's hemoglobin. Plasmodia, which lack heme oxygenases, detoxify heme by sequestering it into an insoluble heme aggregate termed malarial pigment or hemozoin. The quinoline-based family of antimalarials interfere with this process by an as yet unknown mechanism that has recently come under intense scrutiny as part of the effort to combat the spread of chloroquine-resistant strains of Plasmodium. A variety of spectroscopic and bioanalytical techniques indicate that hemozoin is similar to the synthetic aggregated heme phase {beta}-hematin, which is thought to form strands of hemes linked by propionate oxygen-iron bonds as well as interstrand propionate hydrogen bonds. Characterization of the carboxylate stretching bands for the propionic acid side chains by IR and Raman spectroscopy provides the best evidence for the presence of iron-oxygen bonds to the propionate side chains. Unfortunately, crystallographic characterization of these heme aggregates has been hampered by the phase heterogeneity of many synthetic preparations as well as by the small size of the synthetic and natural crystallites isolated from either trophozoites and infected hosts. High resolution powder diffraction has been used extensively for the solution of many structural problems, and it can solve problems posed by diffraction from microcrystalline phases. In this communication we describe the characterization of {beta}-hematin derived from both synthetic and natural sources and provide new unambiguous evidence that the heme aggregate present in late stage trophozoites is {beta}-hematin. In a process inhibited by the quinoline antimalarial drugs, Plasmodia detoxify heme released during the degradation of hemoglobin by aggregating it into malarial pigment, an insoluble crystalline heme coordination polymer. Synchrotron x-ray powder diffraction patterns for intact desiccated malarial trophozoites and synthetic {beta}-hematin have been measured; both materials correspond to a single crystalline triclinic lattice with unit cell parameters a = 12.2176(4), b = 14.7184(5), c = 8.0456(3) {angstrom}; {alpha} = 90.200(2), {beta} = 96.806(3), {gamma} = 97.818(3){sup o} and Z = 2. These results unambiguously demonstrate that hemozoin crystallites are identical to synthetic {beta}-hematin.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 929999
- Report Number(s):
- BNL-80610-2008-JA; JBCHA3; TRN: US200822%%1152
- Journal Information:
- Journal of Biological Chemistry, Vol. 272, Issue 2; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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