Mark Mayhew

Characterization of a Receptor for Heat Shock Protein 70 on Macrophages and Monocytes

Abstract Heat shock proteins (Hsps) and molecular chaperones isolated from tumors or virally infected cells elicit an efficient CD8+ T cell response against bound antigenic peptides. This immune response is mediated by presentation of the peptides on MHC class I complexes of antigen-presenting cells (APCs), but the cellular mechanism of this presentation process is not yet understood. Here we provide evidence for the existence of a proteinaceous receptor on the surface of APCs that is specific for mammalian Hsp70. Using a flow cytometry-based assay, saturable binding of Hsp70 to the cell surface of macrophages and peripheral blood monocytes, but not of lymphocytes, can be demonstrated. The affinity of the receptor is in the sub-micromolar range (Kd < 100nm). Only mammalian Hsc70/Hsp70, but not bacterial Hsp70, is bound with high affinity. Subsequent to binding, Hsp70 is taken up by endocytosis, resulting in an intracellular localization. Our results suggest that receptor-mediated endocytosis forms the basis for the demonstrated efficacy of Hsp70-peptide complexes as anti-tumor vaccines.

Role of Prokaryotic Chaperonins in Protein Folding

Publisher Summary This chapter discusses the role of prokaryotic in protein folding. The important role that molecular chaperones play in mediating cellular protein folding and assembly has only recently come to light. This is remarkable, given the fundamental biological significance of protein folding. However, the long-held view that both in vitro and in vivo protein folding are spontaneous processes provided an elegantly simple explanation of a very complex problem. Indeed it is astonishing that the Escherichia coli protein GroEL, which has been studied for over two decades, has only in the past few years been demonstrated to mediate the folding of a large fraction of cytosolic proteins. Understanding of protein folding and oligomeric assembly has been primarily derived from three lines of investigation: the analysis of the assembly of the enzyme ribulose-bisphosphate carboxylase-oxygenase in chloroplasts, the analysis of protein folding in mitochondria, and the in vitro reconstitution of a pathway of chaperone-mediated protein folding, which appears to occur generally in the cytosol of bacteria and eukaryotic cells. Detailed models for the GroEL/ GroES reaction cycle have been proposed and are now being tested experimentally. The three-dimensional structure of GroEL, enables knowledge based mutagenesis to be carried out, providing us with more specific information on the structure-function relationships within GroEL.