Title: Allosteric Coupling, Nucleotide Binding and ATP Hydrolysis by Hsp70 Chaperones on a Structural Basis
Description: Healthy cells continuously produce proteins to accomplish various functions, including immune responses, reaction catalyses, transmitting signals, structural supports and molecular transport. Protein needs to fold correctly into three-dimensional shape in order to function well, using the information stored in the amino acid sequence. Proteins may fold spontaneously in solution, but the situation in living cells can be complicated. Cells are filled with nucleic acids and proteins thus they are usually in a stressful environment. Under such circumstances, proteins can be unfolded or misfolded, leading to non-function or even toxicity. Cells employ molecular chaperones to solve protein folding problems. Among the many types of chaperones, heat shock proteins of approximately 70KDa (Hsp70s) act as a hub, because its functions feed into other members of the chaperone network. Hsp70s help to stabilize nascent polypeptides, facilitate cross-membrane translocation, refold the misfolded proteins, and guide non-recoverable denatured proteins to degradation.

Hsp70s have explicit role in cancer cells, because elevated metabolism requires increased Hsp70s’ activity to avoid apoptosis and ensure survival. Hsp70s also help to prevent neurodegenerative diseases, and decreased level of Hsp70s is found in age-related symptoms and diseases. In general, it is well understood what Hsp70s can do, but little is known how Hsp70s do the job. Hsp70s are present and highly conserved in all living species, comprised of two structural domains. The nucleotide binding domain (NBD) binds and hydrolyzes ATP, while the substrate binding domain (SBD) binds and releases hydrophobic peptides. Although Hsp70s are known to act as an allosteric molecular machine, the details are elusive about how the domains are regulated. Besides, how nucleotide binding affects the Hsp70s’ function, and how ATP hydrolysis is performed are also unknown. In this thesis, I first introduce salient background on the Hsp70 subject, then explore previously unclear aspects of Hsp70 allosteric regulation and catalytic activity in two chapters describing my dissertation research, and finally conclude with my perspectives on future directions.