ABSTRACT
The 70 kDa heat shock related proteins (referred to generically as “Hsp70s” in this chapter-taken to include the endoplasmic reticulum-resident BiPs, cytoplasmic/ nuclear Hsc70s, prokaryotic DnaKs and others) comprise a family of molecular chaperones that are essential for cell viability. Their biochemical and biological functions are discussed in depth in several chapters of this volume, and hence they will not be elaborated extensively here. In brief, the Hsp70s cyclically bind and release “unstructured” segments of polypeptides; the binding presumably suppresses aggregation or misfolding of the peptide segments, while their release gives them the opportunity to coalesce into a correctly folded tertiary structure. The kinetics of the binding and release cycle is modulated by ATP/ADP; in the presence of ATP, peptide release is relatively rapid, while in the presence of ADP, Hsp70-peptide complexes are stable and long-lived. In vivo, unstructured segments of polypeptide may present themselves in many different contexts ranging from nascent polypeptides emerging from ribosomes during translation (Beckmann et al., 1990; Hartl, 1996; Welch et al., this volume),
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1. Introduction 2. Structure 3. ATPase Activity 4. Coupling of the ATPase Activity to the Peptide Binding Actitivity 5. Modulation of Hsp70 Activity 5.1. Self-association 5.2. Posttranslational Modification 5.3. Accessory Proteins 6. Epilogue 7. References
polypeptides translocating across membranes into intracellular organelles (Scherer et al., 1990; Schatz and Dobberstein, 1996; chapter in this volume by Welch et al.; Haas and Zimmermann; Dekker and Pfanner; Muckel and Soll) and protein denaturation (e.g. heatdenatured proteins arising from thermal stress of cells (Skowyra et al., 1990; Li et al., this volume).
