No description available.

The multi-functional FGL2 can be expressed as either a type II membrane-associated glycoprotein or a secreted tetrameric molecule. As an important effector of regulatory T cells, secreted FGL2 inhibits dendritic cell maturation and T cell proliferation. The mechanism of its immunomodulatory function remains unclear. The goals of this thesis are to identify receptor(s) of secreted FGL2, key biological functions and signaling pathways, and mechanism of FGL2 oligomerization. Soluble FGL2 was critical for all studies, and the production of recombinant FGL2 was compared in E. coli, insect cells and mammalian cells. Soluble and stable FGL2 was secreted only by mammalian cells, indicating the importance of post-translational modification. In flow cytometry and surface plasmon resonance assays, recombinant FcFGL2 and albumin tagged FGL2 fusion proteins bound to Fc gamma RIIB and Fc gamma RIII receptors expressed by antigen presenting cells (APCs), including lipopolysaccharide (LPS)-stimulated B lymphocytes, endothelial cells, thioglycollate-stimulated peritoneal macrophages, and bone marrow-derived dendritic cells (BM-DCs). The binding of recombinant FGL2 to Fc gamma RIIB and Fc gamma RIII was specific, dependent on receptor expression and blocked by anti-Fc gamma RIIB/III antibody. FcFGL2 inhibited the maturation of BM-DC derived from fc gamma riib wild type mice but not from fc gamma riib knock out mice. It also induced apoptosis of the A20 mouse B cell line (Fc gammaRIIB+), but not the A20IIA1.6 cell line (Fc gamma RIIB-). The activation of caspases induced by FcFGL2 binding to A20 cells was confirmed by flow cytometry, Western blotting and analysis of DNA fragmentation. The role of Fc gammaRIIB in FGL2-mediated immunosuppression was confirmed in vivo. Infusion of FcFGL2 into fc gamma riib+/+, but not fc gamma riib-/- C57BL/6J mice (H-2b) inhibited the rejection of fully mismatched BALB/cJ (H-2d) skin and heart allografts. Studies on the mechanism of FGL2 oligomerization employed site-directed mutagenesis and revealed that cysteines at positions 94, 97, 184, and 187 were critical. Mutation of these cysteines resulted in secretion of monomeric FGL2. Computer modeling of FGL2 tetramers predicted an asymmetric arrangement that was similar to the structure of multimeric ficolin. The data presented in this thesis provide mechanistic insights into the immunosuppressive activity of soluble FGL2, and a foundation for the development of a novel and potentially highly effective immunosuppressive therapy.

The multi-functional FGL2 can be expressed as either a type II membrane-associated glycoprotein or a secreted tetrameric molecule. As an important effector of regulatory T cells, secreted FGL2 inhibits dendritic cell maturation and T cell proliferation. The mechanism of its immunomodulatory function remains unclear. The goals of this thesis are to identify receptor(s) of secreted FGL2, key biological functions and signaling pathways, and mechanism of FGL2 oligomerization. Soluble FGL2 was critical for all studies, and the production of recombinant FGL2 was compared in E. coli, insect cells and mammalian cells. Soluble and stable FGL2 was secreted only by mammalian cells, indicating the importance of post-translational modification. In flow cytometry and surface plasmon resonance assays, recombinant FcFGL2 and albumin tagged FGL2 fusion proteins bound to Fc gamma RIIB and Fc gamma RIII receptors expressed by antigen presenting cells (APCs), including lipopolysaccharide (LPS)-stimulated B lymphocytes, endothelial cells, thioglycollate-stimulated peritoneal macrophages, and bone marrow-derived dendritic cells (BM-DCs). The binding of recombinant FGL2 to Fc gamma RIIB and Fc gamma RIII was specific, dependent on receptor expression and blocked by anti-Fc gamma RIIB/III antibody. FcFGL2 inhibited the maturation of BM-DC derived from fc gamma riib wild type mice but not from fc gamma riib knock out mice. It also induced apoptosis of the A20 mouse B cell line (Fc gammaRIIB+), but not the A20IIA1.6 cell line (Fc gamma RIIB-). The activation of caspases induced by FcFGL2 binding to A20 cells was confirmed by flow cytometry, Western blotting and analysis of DNA fragmentation. The role of Fc gammaRIIB in FGL2-mediated immunosuppression was confirmed in vivo. Infusion of FcFGL2 into fc gamma riib+/+, but not fc gamma riib-/- C57BL/6J mice (H-2b) inhibited the rejection of fully mismatched BALB/cJ (H-2d) skin and heart allografts. Studies on the mechanism of FGL2 oligomerization employed site-directed mutagenesis and revealed that cysteines at positions 94, 97, 184, and 187 were critical. Mutation of these cysteines resulted in secretion of monomeric FGL2. Computer modeling of FGL2 tetramers predicted an asymmetric arrangement that was similar to the structure of multimeric ficolin. The data presented in this thesis provide mechanistic insights into the immunosuppressive activity of soluble FGL2, and a foundation for the development of a novel and potentially highly effective immunosuppressive therapy.

No description available.

No description available.

Dyslipidemia often accompanies metabolic diseases such as obesity and type II diabetes mellitus and represents a risk factor for cardiovascular disease. Clearance of triglycerides from the plasma is mediated by lipoprotein lipase (LPL), which hydrolyzes the triglycerides in chylomicrons and VLDL, liberating fatty acids for tissue uptake. LPL functions in the capillaries of the heart, adipose tissue, and skeletal muscle where LPL is anchored to the capillary wall by its endothelial cell transporter GPIHBP1. LPL activity is regulated by several factors including three members of the angiopoietin-like (ANGPTL) family–ANGPTL3, ANGPTL4, and ANGPTL8. How these proteins interact with LPL, especially in the physiological context of LPL anchored to endothelial cells by GPIHBP1, has not been well characterized. In my studies of ANGPTL4, I found when LPL is bound to GPIHBP1, it is partially, but not completely, protected from inactivation by ANGPTL4. Inactivation of LPL by ANGPTL4 leads to the dissociation of active LPL dimers into inactive monomers and I found that these monomers have a greatly reduced affinity for GPIHBP1. ANGPTL4 can be cleaved in vivo, separating the N-terminal coiled-coil domain from the C-terminal fibrinogen like-domain. I found the N-terminal domain alone is a much more potent LPL inhibitor than the full-length protein, even though both appear to have similar binding affinities for LPL-GPIHBP1 complexes. When I investigated ANGPTL3, I found ANGPTL3 itself is not a potent inhibitor of LPL at physiological concentrations, and unlike ANGPTL4, cleavage of ANGPTL3 does not improve its ability to inhibit LPL. Instead I found that ANGPTL3 forms a complex with ANGPTL8, a complex that only forms efficiently when the two proteins are co-expressed, and that this complex allows ANGPTL3 to bind and inhibit LPL. My data provide new insights into how ANGPTL proteins regulate LPL activity and the delivery of fat to tissues.

Ubiquitin fold modifier 1 (Ufm1) is a member of the ubiquitin like protein (UBL) family. Like other UBLs, Ufm1 can be conjugated to protein substrates via specific E1 (Uba5), E2 (Ufc1) and E3 (Ufl1) enzymes, and removed from these substrates via the action of Ufm1-specific proteases. While Ufm1 has been implicated in endoplasmic reticulum (ER) function, its biological roles remain poorly understood. By identifying; (a) Ufm1 binding proteins, (b) protein interactors of the Ufm1 conjugation/deconjugation system, (c) Ufm1 conjugates, as well as (d) the intracellular localization of Ufm1 and its main interactors, I aimed to better characterize the biological role(s) of this poorly understood UBL.

Ubiquitin fold modifier 1 (Ufm1) is a member of the ubiquitin like protein (UBL) family. Like other UBLs, Ufm1 can be conjugated to protein substrates via specific E1 (Uba5), E2 (Ufc1) and E3 (Ufl1) enzymes, and removed from these substrates via the action of Ufm1-specific proteases. While Ufm1 has been implicated in endoplasmic reticulum (ER) function, its biological roles remain poorly understood. By identifying; (a) Ufm1 binding proteins, (b) protein interactors of the Ufm1 conjugation/deconjugation system, (c) Ufm1 conjugates, as well as (d) the intracellular localization of Ufm1 and its main interactors, I aimed to better characterize the biological role(s) of this poorly understood UBL.

<p> Amoeboid Motion is thought to be due to the action of an actomyosin- like protein present in the cytoplasm of amoeba. A co-ordinated net- 0 work of microfilaments of the actomyosin-like protein, 70 A in diameter, may be the mechanical means of accomplishing amoeboid motion. The microfilaments formed of the actomyosin-like protein, may be capable of rapid association and dissociation in vivo. In this thesis, the cytoplasm of Naegleria gruberi amoeba has been shown to possess a protein similar to actomyosin. Characterization of the ATPase activity, superprecipitating ability, electrophoretic behaviour and microfilament producing ability reveal that the actomyosin-like protein of Naegleria gruberi amoeba is quite similar to the analogous protein in Physarum polycephalum. Naeqleria gruberi may be an ideal organism in which to study the interconversion of one form of a biologically active macromolecule to another., In different stages of the life cycle, amoeboid motion, flagellar beating and mitotic spindles are present. It is possible that the same contractile molecules in different forms may perform different functions. </P> / Thesis / Master of Science (MSc)

Brucella abortus is a facultative, intracellular zoonotic pathogen, which can cause undulant fever in humans and abortion in cattle. Despite all of the progress in brucellosis research, there are still many unanswered questions regarding the molecular mechanisms involved in the pathogenesis of Brucella infections. To better understand the Brucella antigens involved in virulence and/or immunity, genetic and immunologic characterization of a 16 kDa protein of B. abortus was performed. Using PCR methods, the gene encoding the 16 kDa protein was cloned and sequenced. PCR and Southern blot analysis revealed that the gene is conserved among the 6 nomen species of Brucella. Overexpression of this protein in B. abortus vaccine strain RB51 was achieved using Brucella groE and sodC promoters as well as its own promoter. Protection and clearance studies were performed in mice to determine the role of this protein in Brucella immunity and pathogenesis. Inoculation with either strain RB51 overexpressing the 16 kDa protein or a DNA vaccine encoding the 16 kDa protein gene failed to provide significant protection. No difference was noted between the splenic clearance of B. abortus strain 2308 and its recombinant overexpressing the 16 kDa protein. A mutant of strain 2308 (2308D16) was created by disrupting the 16 kDa protein's gene with a chloramphenicol resistance cassette. Western blot analysis indicated that the O antigen profile of strain 2308D16 differed from that of strain 2308. Mice cleared strain 2308D16 faster than strain 2308 indicating the potential attenuation of the disruption mutant. Purified 16 kDa protein was obtained by overexpressing it in E. coli via the pRSET expression system. Western blotting results initially identified this protein as an immunoglobulin-binding protein. Hemagglutination assay revealed that the 16 kDa protein exhibits lectin-like properties. Preliminary studies using hemagglutination inhibition identified mannose as a possible sugar to which the 16 kDa protein can interact. The lectin-like properties exhibited by the 16 kDa protein appears to influence smooth lipopolysaccharide production, and thereby may be involved in virulence. / Master of Science