Regulation of Hsp70 Function by HspBP1Structural Analysis Reveals an Alternate Mechanism for Hsp70 Nucleotide Exchange

Abstract

HspBP1 belongs to a family of eukaryotic proteins recently identified as nucleotide exchange factors for Hsp70. We show that the S. cerevisiae ortholog of HspBP1, Fes1p, is required for efficient protein folding in the cytosol at 37 degrees C. The crystal structure of HspBP1, alone and complexed with part of the Hsp70 ATPase domain, reveals a mechanism for its function distinct from that of BAG-1 or GrpE, previously characterized nucleotide exchange factors of Hsp70. HspBP1 has a curved, all alpha-helical fold containing four armadillo-like repeats unlike the other nucleotide exchange factors. The concave face of HspBP1 embraces lobe II of the ATPase domain, and a steric conflict displaces lobe I, reducing the affinity for nucleotide. In contrast, BAG-1 and GrpE trigger a conserved conformational change in lobe II of the ATPase domain. Thus, nucleotide exchange on eukaryotic Hsp70 occurs through two distinct mechanisms.

De novo 19q13.42 duplications involving NLRP gene cluster in a patient with systemic-onset juvenile idiopathic arthritis

“…23 In several experimental models, T cells responding to Hsps play an important role in the regulation of peripheral tolerance and suppressing pathogenic immune response. 24 HspBP1 (Hsp70 binding protein 1) has an inhibitory effect in Hsp70-assisted refolding reactions in the cytosol, 25,26 suggesting that HspBP1 plays an important role in regulating immune responses. HspBP1 duplication may alter immune responses in the s-JIA patient.…”

The yeast Hsp110, Sse1p, exhibits high‐affinity peptide binding

“…Unlike Hsp70s, however, Hsp110s do not actively fold proteins, but rather act as holdases to maintain the solubility of denatured model protein substrates [3,[5][6][7]. Hsp110s also function as NEFs for Hsp70s [3,8,9]. Hsp110s most likely play an important role in protein homeostasis because deletion of the predominant cytoplasmic Hsp110 in yeast, SSE1, leads to a slow growth phenotype [10,11], and because Hsp110 over-expression in mammalian tissue culture cells confers thermotolerance [6].…”

Structure and function of Hip, an attenuator of the Hsp70 chaperone cycle

“…All structures are shown in ribbon representation and presented on the same scale. PDB accession numbers are as follows: 1DKG (Harrison et al, 1997), 1HX1 (Sondermann et al, 2001), 1XQS (Shomura et al, 2005) and 3D2F (Polier et al, 2008).…”

“…The structure of the core fragment of HspBP1 has an all-α-helical structure containing four armadillo repeats ( Fig. 7) (Shomura et al, 2005). In contrast to the other NEFs, HspBP1 binding to the NBD causes much more drastic structural changes.…”

“…Figure 37A shows that the binding surfaces on the Hsp70 NBD strongly overlap, suggesting mutually exclusive binding of Hip and NEFs to Hsp70 (Polier et al, 2008;Schuermann et al, 2008;Shomura et al, 2005;Sondermann et al, 2001;Xu et al, 2008). First we tested the stimulatory effect of NEFs on the MABA-ADP dissociation from the Hsp70N•MABA-ADP complex in the absence of Hip.…”