research
hajduk lab
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research hajduk lab |
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research positions the lab |
Biochemistry and Molecular Biology of Parasitic Diseases.
Figure 1. Giemsa Stained Bloodstream Trypanosoma brucei brucei. Blood smear from infected mouse containing both long slender (center and right) and short stumpy (left) parasites. The mitochondrial DNA (kinetoplast (k)) and nucleus (n) stain intensely with Giemsa due to the presence of DNA.
RNA Processing and Trafficking in Trypanosomes. Mitochondrial mRNAs in trypanosomes are often modified post-transcriptionally by the insertion or deletion of uridines. This process, termed RNA editing, can result in the precise addition of hundreds of uridines at specific sites in the mRNAs creating functional open reading frames (Figure 2). We are investigating the mechanism of RNA editing and the assembly of proteins and RNAs required for editing. Recently, we discovered that alternative editing of mRNAs can create novel open reading frames and protein products. The protein encoded by the first alternatively edited mRNA identified, Alternatively Edited Protein-1 (AEP-1) is involved in the maintenance of the unusual mitochondrial DNA of trypanosomes call the kinetoplast. We have also have initiated studies on the developmental regulation of RNA editing and the evolutionary origins of this unusual from of RNA processing.
Figure 2. RNA Editing of mRNA in Trypanosomes. RNA editing in trypanosome mitochondria is a multi-step enzymatic cascade involving several enzymes and RNAs. The information for the correct insertion or deletion of uridines is encoded by guide RNAs (gRNAs). Formation of a binary complex of gRNA and pre-mRNA is required to initiate an enzymatic cascade of endonuclease cleavage, uridine specific addition by a terminal uridyl transferase, and RNA ligation My laboratory is also interested in the pathway of RNA trafficking from the nucleus to the mitochondria in trypanosomes. We discovered that all of the mitochondrial tRNAs are encoded by nuclear genes. To carry out mitochondrial protein synthesis at least 20 tRNAs are imported from the cytoplasm. The biochemical requirements for RNA import into mitochondria have not been well established and we have developed in vitro and in vivo assays to study the biochemical requirements and the RNA sequences or structures required for RNA import into mitochondria. Recently, we have found that precursor tRNAs are selectively imported and several cis-acting elements have been identified that enhance import. The goals of this research are to identify both the cis-acting elements in the tRNAs that direct mitochondrial import and also the components of mitochondrial translocation machinery. (Research supported by NIH AI21401 and NIH AI61356) Non-immune Killing of Trypanosomes by Human High Density Lipoproteins. Innate immunity can play an important role in preventing or limiting the effects of a parasitic infection. We are particularly interested in the biochemical and molecular basis for the non-immune killing of African trypanosomes. Trypanosoma brucei brucei is the causative agent of a bovine disease Nagana, and is killed by a toxic subspecies of human serum high-density lipoproteins (HDL) (Figure 3) while the human sleeping sickness parasites, T. b. gambiense and T .b. rhodesiense are not. Our studies mainly focus on the biochemical composition of this unique human HDL subclass and the mechanism of trypanosome killing. We have also begun to investigate the mechanism of human infectivity by the human sleeping sickness trypanosomes. (NIH AI39033 and NIH AI 54596.
Figure 3. Trypanosome lytic factor (TLF) is a minor subclass of human HDL. This minor subclass of HDL is composed of apolipoprotein AI, apolipoprotein LI and haptoglobin related protein (Hpr). TLF kills T. b. brucei following binding, endocytosis and lysosomal localization. FUNDING Grant Funding for the Hajduk Laboratory: R01 AI 21401 (Years 20-24) (Hajduk) 6/15/03-11/30/08 RO1 AI 61356 (Years 1-5) (Hajduk) 4/01/05 – 3/31/10
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