Functional and structural characterization of Hsp110, a nucleotide exchange factor of the molecular chaperone Hsp70
Final Report Abstract
Protein folding and complex assembly are crucial processes in eukaryotic cells. Molecular chaperones accomplish these tasks by recognizing folding intermediates and by prevention of protein aggregation. In the DFG-funded project, the molecular basis of the regulation of the general purpose molecular chaperone Hsp70 by the nucleotide exchange factor (NEF) Hsp110 was studied. A nucleotlde-dependent conformational cycle forms the basis for the folding activity of Hsp70. In complex with ADP, Hsp70 tightly binds to unfolded substrate proteins; in the ATP-bound state however, substrate Interactions with Hsp70 are highly dynamic. Cochaperones like J-domain proteins and NEFs regulate the transition between these states by stimulating ATP hydrolysis and release of ADP from Hsp70, respectively. Three distinct classes of Hsp70 NEFs are present in eukaryotic cells: BAG domain proteins, HspBP1 and Hsp110 homoiogs. These factors are only partially redundant, suggesting functional diversification. In the present work, the crystal structure of a functional complex between the S. cerevisiae Hsp110 homolog Sselp and the nucleotide binding domain of human Hsp70 was determined. Hsp110 proteins are remote sequence homolog of Hsp70 and have the same principal domain composition, consisting of an N-termlnal nucleotide binding domain (NBD), a ß-sandwich domain and a 3-helix bundle domain. In contrast to the present structures of canonical Hsp70s, Sse1p has a compact conformation, In which ß-sandwich domain and a 3-helix bundle domain are arranged around the NBD. In the complex with Hsp70, Sse1p embraces the NBD of Hsp70, stabilizing an open conformation with low affinity for ADP. An extensive mutational analysis confirmed the observed binding mode and showed that Hsp110 proteins principally function as nucleotide exchange factors of Hsp70. In contrast to other NEF classes, direct Interactions of the substrate protein with Hsp110 may furthermore support Hsp70-asslsted folding in a cooperative manner. Preliminary data suggest that the substrate binding mode of Hsp110 proteins might differ from that observed with canonical Hsp70s.
Publications
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(2008) Structural basis for the Cooperation of Hsp70 and Hsp110 chaperones in protein folding. Cell 133,1068-1079
Polier, S., Dragovic, Z., Hartl F.U. and Bracher A.
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(2009) Proteinfaltung in der Zelle - eine komplexe Angelegenheit. Biospektrum 15, 255-257
Polier, S. and Bracher, A.
