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The ability of members of the hsp70 family to bind to peptides in vivo and in vitro suggests that they may be involved in the processing of antigens for binding to Major Histocompatibility (MHC) class I and/or class n molecules. The aims of this thesis have been to provide evidence for the involvement of hsp70s in antigen processing and to characterise the binding of peptides by hspTOs by structural and functional studies. Firstly, the peptide-binding domains of two hsp70s, hsp70hom and PBP74, were expressed in isolation from the rest of the molecule for structure determination. Both of these hsp70s were implicated in antigen processing: hsp70hom in the class I pathway, due to its cytoplasmic localisation and constitutive expression, and the presence of its gene in the MHC; and PBP74 in the class n pathway because published work indicated that it was localised to endosomes and that antibodies against it inhibited antigen processing. The expression and purification of both peptide-binding domains was very successful, and one dimensional NMR experiments indicated that they were folded. However, it was not possible to determine their structures by NMR spectroscopy or X-ray crystallography because they aggregated in solution at high concentrations. Instead, the structure of the C-terminal region of hsp70hom, which includes its peptidebinding domain, was modelled based on the known structure of the equivalent portion of dnaK, the hsp70 of E.coli. The structure of hsp70hom is predicted to be very similar to that of dnaK, and modelling studies suggest that it is likely to bind peptides in a closely related fashion. The modelling of complexes between hsp70hom and two peptides suggest that the peptide-binding groove is very versatile, accounting for the broad peptide-binding specificity of hsp70s. The interactions of hsp70hom and PB74 with peptides were investigated using plate binding assays and isothermattitration calorimetry. A biotinylated peptide bound to the peptide-binding domain of hsp70hom, immobilised in plastic wells, with a Kd of <25 μM, which is within the range of Kds reported for other hsp70-peptide complexes (0.1-100 μM). In solution, isothermal titration calorimetry showed that the binding of peptides to the peptide-binding domains of hsp70hom and PBP74 was likely to be entropically rather than enthalpically driven, and, therefore, the interactions involved are likely to be predominantly hydrophobic. Secondly, PBP74, an hsp70 thought to be involved in the class II antigen processing pathway in endosomes, was localised by immunofluorescence microscopy. It was shown to be a mitochondrial protein, and is, therefore, unlikely to be involved in antigen processing. The presence of other members of the hsp70 family in lysosomes purified from a B cell line by Percoll density gradient centrifugation was investigated using antibodies that reacted with many Afferent members of the hsp70 family. No hsp70s were detected in these late endocytic compartments, even after heat shock or serum starvation. However, the presence of an hsp70 in endosomes, or of a member of this family not detected by the antibodies used, in lysosomes, cannot be ruled out. A third approach investigated the induction of the three hsp70 genes found in the MHC by four cytokines. The hsp70-l and hsp70-2 genes are induced at the mRNA level by IFN-γ and IL- 1, while TNF induces hsp70-2 alone. This data supports a role for the heat-inducible hsp70 in MHC class I antigen processing, as it appears to be coregulated with known members of this antigen processing pathway. The expression of hsp70hom was unaffected by any of the four cytokines examined. In addition, the mitochondrial hsp70 (which is not encoded in the MHC) appears to be induced by IFN-γ at the protein level. The research presented in this thesis provides a greater understanding of the peptide-binding properties of two hsp70s. Further work is necessary to show conclusively whether any of the hsp70s is involved in antigen processing.

This thesis describes studies on the binding of peptides to the murine major histocompatibility complex (MHC) class I molecule H-2D^b (D^b). The expression of the recombinant soluble D^b molecule in Chinese hamster ovary cells and its subsequent purification by nickel affinity chromatography, gel filtration, and preparative native isoelectric focusing are reported. The product is the correct molecule, homogeneous, a dimer of dimers, and free of endogenous peptide. A novel binding assay based on the enhancement of natural tryptophan fluorescence by the binding of peptide is introduced. This assay is used to determine melting curves of the empty and peptide-loaded protein, and to measure association rate constants by stopped-flow fluorescence spectroscopy. Radioligand binding measurements of equilibrium as well as association and dissociation rate constants and their temperature dependence are reported. In agreement with earlier observations, the ratio of association and dissociation rate constants is much larger than the equilibrium association constant. Fluorescence anisotropy decay spectroscopy gives evidence for conformational alterations in the D^b molecule upon peptide binding. The data, possible errors and ways to avoid them, and mathematical models of binding are discussed to obtain an overall picture of the binding process.

Host antigen presenting cells (APC) are known to be critical for the induction of graft versus host disease (GVHD) after allogeneic bone marrow transplantation (BMT) but the relative contribution of specific APC subsets remains unclear. We have studied the role of host B cells in GVHD by using B cell deficient (ìMT) mice as bone marrow transplant recipients in a model of CD4 T cell-dependent GVHD to major histocompatibility antigens. We demonstrated that acute GVHD is initially augmented in ìMT recipients relative to wild-type (WT) recipients (mortality: 85% v 44%, P<0.01) and that this was the result of an increase in donor T cell proliferation, expansion and inflammatory cytokine production early after BMT. Recipient B cells were depleted 28-fold at the time of BMT by total body irradiation (TBI) administered 24 hours earlier and we demonstrated that TBI rapidly induced sustained IL-10 generation from B cells but not dendritic cells (DC) or other cellular populations within the spleen. Finally, recipient mice in which B cells were unable to produce IL-10 due to homologous gene deletion developed more severe acute GVHD than recipient mice in which B cells are WT. Thus the induction of interlukin-10 (IL-10) in host B cells during TBI attenuates experimental acute GVHD.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains x, 117 p.; also includes graphics (some col.) Includes bibliographical references (p. 99-117). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Chicago. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Case Western Reserve University, 2007. / [School of Medicine] Department of Molecular Biology and Microbiology. Includes bibliographical references. Available online via OhioLINK's ETD Center.

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