Analysis of molecular chaperone activities using in vitro and in vivo approaches.

1. Introduction Molecular chaperones function in a range of protein homeostatic events, including cotranslational protein folding, assembly and disassembly of protein complexes, and protein transport across membranes. Many molecular chaperones are also known as heat-shock proteins, which refers to their regulation by stress conditions as diverse as infection with viral and bacterial agents, exposure to transition heavy metals, heat shock, amino acid analogs, drugs, toxic chemicals, and pathophysiologic and disease states including oxidative stress, fever, inflammation, infection, myocardial stress and ischemia, neuro-degenerative diseases, aging, and cancer. The heat-shock response through the elevated expression of heat-shock proteins (Hsp's) protects cells and tissues against the deleterious effects of stress. Pre-exposure to mild, nontoxic stresses such as lower heat-shock temperatures, and reduced levels of metals, arsenite, ethanol, or oxidants confers a transient resistance (thermotolerance) to a subsequent , otherwise lethal, exposure to stress. A common feature of most, if not all, stresses against which Hsp's have protective capacity are effects on protein folding and protein aggregation. Molecular chaperones represent a large class of proteins including Hsps 110, 104, 90, 70, 60, 40 (hdj-1), and 27, which are functionally related based on common properties of influencing the conformation and activities of protein substrates (1) (see also Chapter 25, this volume). Generally, molecular chaperones discriminate among distinct folded states of a substrate protein and interact with only a subset of these states (e.g., non-native intermediates) to influence folding pathway kinetics. Whereas some chaperones such as Hsp70