During the pathogenic blood stage of a malaria infection, the Plasmodium parasites degrade hemoglobin as a source of nutrition. As a consequence, free heme, known to be toxic to the parasite, is released. It is believed that the parasite circumvents heme toxicity by sequestering the heme molecules into a dark brown crystalline material known as hemozoin. The molecular details associated with the formation of hemozoin and its synthetic counterpart, beta-hematin, are presented in this dissertation. Firstly, the biological mediator of hemozoin formation was investigated. Neutral lipid droplets (NLDs) were shown to be sufficient at mediating the production of brown pigments that are morphologically and chemically identical to hemozoin. Optimal partitioning of heme into NLDs was pH dependent with maximal heme conversion at a pH condition similar to that of the parasites digestive food vacuole, the biological site of crystallization. The rate of beta-hematin formation was rapid enough to protect the parasite from heme toxicity. Secondly, the interfacial interactions between lipid molecules and heme were investigated using Langmuir-Blodgett monolayer creation techniques. Comparisons of these surface pressure-area isotherms revealed that the biological composition of neutral lipid is characterized by disordered packing of lipids. This fluid lipid surface may account for the low activation energy measured for beta-hematin formation associated with NLDs. Substituted protoporphyrin IX compression studies suggest that hemozoin nucleation begins when the propionic group of a heme unit anchors to the polar head group of the lipid molecules. Thirdly, crystallization parameters associated with beta-hematin formation was examined using various solvent conditions to facilitate heme solubility. The formation of beta-hematin using the aprotic solvent dimethylsulfoxide and some polyethyleneglycols demonstrates that crystallization is accelerated by increasing heme solubilization in acidic conditions, resulting on increased dispersion of amorphous heme precipitates. Crystallization data support the notion that modulation of the water activity is important mechanism to support spontaneous heme crystallization. Futhermore, through proper manipulation of solvent properties, the morphologies of beta-hematin can be controlled. Finally, beta-hematin crystals were applied to phage display technologies to identify short peptide sequences that specifically recognize select crystal face. Isolated peptides were sufficient at mediating beta-hematin formation.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-07272010-151453 |
| Date | 28 July 2010 |
| Creators | Hoang, Anh Ngoc |
| Contributors | Dr. Kane Jennings, Dr. Todd Giorgio, Dr. David Cliffel, Dr. David Wright, Dr. Rick Haselton |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu//available/etd-07272010-151453/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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