Interaction of structurally diverse HSPs with ligand binding domains of CD91 (APP2P.110)

Select members of the Heat Shock Proteins (HSPs) are molecular chaperones, carrying diverse cargo including nucleotides, lipids, misfolded proteins and peptides. Immunization of mice or humans with HSPs leads to priming of T cell responses specific for the peptide antigens that they chaperone. HSPs, with the chaperoned peptides, in the extracellular environment have been shown to associate with the cell surface receptor CD91 expressed on antigen presenting cells (APCs). CD91 on APCs allow for endocytosis of HSP-peptide complexes and cross-presentation. Recently, we discovered that the same receptor CD91 acts as a signaling receptor for HSPs. HSPs were shown to cause the phosphorylation of the cytoplasmic tail of CD91, and thereby dictate the release of cytokines in a CD91-dependent manner. In this study, we aim to identify the domains on CD91 that are necessary for HSP binding. CD91 is expressed as a single polypeptide chain in the ER that is cleaved into the extracellular 515 kDa α-chain, included four ligand-binding domains, and the 85 kDa β-chain. By creating mini-gene constructs representing the ligand binding domains of CD91, the association of each HSP with each construct can be examined. The completion of this study will explain how the structurally diverse HSPs bind to a single receptor, necessary for priming immune responses.