Disease relevance of HSPA8

• The recombinant 60-kDa fragment of rat hsc70 has been overexpressed in Escherichia coli [1].
• Hsc70-binding peptides selected from a phage display peptide library that resemble organellar targeting sequences [2].

High impact information on HSPA8

• While hydrolysis remains the rate-limiting step in the ATPase cycle, Hip stabilizes the ADP state of Hsc70 that has a high affinity for substrate protein [3].
• We propose a mechanism for the regulation of eukaryotic Hsc70 that is distinct from that of bacterial Hsp70 [3].
• Both BiP and hsc70 have specific peptide binding sites [4].
• Two members of the hsp70 family, termed hsc70 and BiP, have been implicated in promoting protein folding and assembly processes in the cytoplasm and the lumen of the endoplasmic reticulum, respectively [4].
• Uncoating of clathrin-coated vesicles in presynaptic terminals: roles for Hsc70 and auxilin [5].

Biological context of HSPA8

• Structural replacement of active site monovalent cations by the epsilon-amino group of lysine in the ATPase fragment of bovine Hsc70 [6].
• Steady-state solution small-angle X-ray scattering and kinetic fluorescence measurements on a 60-kDa fragment of Hsc70 show that point mutations K71M, E175S, D199S, and D206S in the nucleotide binding cleft impair the ability of ATP to induce a conformational change [7].
• We have examined the roles of Hsc70 and auxilin in the uncoating of clathrin-coated vesicles (CCVs) during neuronal endocytosis [5].
• A fragment containing auxilin's J domain associates in an ATP-dependent reaction with hsc70 to form a complex with a half-life of 8 min at 25 degrees C. When the clathrin binding domain and the J domain are recombined via dimerization of their GST moieties, cofactor activity is partially recovered [8].
• Stable clathrin: uncoating protein (hsc70) complexes in intact neurons and their axonal transport [9].

Anatomical context of HSPA8

• These studies establish that auxilin and Hsc70 participate in synaptic vesicle recycling in neurons and that an interaction between these proteins is required for CCV uncoating [5].
• Although there is very little sequence identity between the two proteins, the structures of rabbit skeletal muscle actin (375-amino acid residues) and the 44-kDa ATPase fragment of the bovine 70-kDa heat shock cognate protein (HSC70; 386 residues) are very similar [10].
• The 70-kDa heat shock cognate (Hsc70) chaperone plays a crucial role in protein (re-)folding and triage in the mammalian cytosol [11].
• Precursor proteins were coimmunoprecipitated from the reticulocyte lysate containing the newly synthesized precursor proteins with an hsc70 antibody [12].
• By using anti-DnaK antibodies we purified the DnaK homologue heat-shock cognate protein (Hsc70) from calf thymus to apparent homogeneity [13].

Associations of HSPA8 with chemical compounds

• In the bovine Hsc70 ATPase fragment, mutation of cysteine 17 or aspartic acid 206 to lysine potentially allows the replacement of an active site potassium ion with the epsilon-amino nitrogen [6].
• We conclude that the hydroxyl of Thr13 is essential for coupling ATP binding to a conformational change in Hsc70 [14].
• We have mutated the equivalent resitude of the bovine heat shock cognate protein (Hsc70), Thr13, to serine, valine, and glycine [14].
• This coupling is proposed to require a glutamate residue, E175 of bovine Hsc70, that is entirely conserved within the Hsp70 family, as it contacts bound Mg2+/ATP and is part of a hinge required for a postulated ATP-dependent opening/closing movement of the nucleotide binding cleft which then triggers substrate release [15].
• Sucrose gradient centrifugation analysis followed by import assay showed that pOTC synthesized in rabbit reticulocyte lysate forms an import-competent complex of about 11S in an hsc70-dependent manner [12].

Physical interactions of HSPA8

• The molecular chaperone Hsc70 assists the in vitro folding of the N-terminal nucleotide-binding domain of the cystic fibrosis transmembrane conductance regulator [16].

Regulatory relationships of HSPA8

• Auxilin also induced polymerization of Hsc70 and bound to the resulting polymer at a 1:1 molar ratio; here too the dissociation constant was 0.6 microM [17].
• In Dex-treated cultures subjected to heat shock, hsc70 antisense RNA blocked the induction of hsp70, indicating that newly synthesized RNA was targeted effectively before it became translationally active [18].
• Hsc70 suppressed eIF-2alpha phosphorylation and maintained the guanine nucleotide exchange activity of eIF-2B in heme-deficient RRL and in hemin-supplemented RRL exposed to elevated temperatures (42 degrees C), denatured protein (reduced carboxymethylated bovine serum albumin, RCM-BSA), oxidized glutathione or Hg2+ [19].

Other interactions of HSPA8

• Ubiquitin-dependent degradation of certain protein substrates in vitro requires the molecular chaperone Hsc70 [20].
• The Hsc70 molecular chaperone effects the uncoating reaction, and is guided to appropriate locations on clathrin lattices by the J-domain-containing co-chaperone molecule auxilin [21].
• In contrast, NIVRKKK was a weaker stimulator of the Hsc70 ATPase activity compared with pigeon cytochrome c peptide and FYQLALT, a peptide optimized for binding to Hsc70 [2].
• Furthermore, we investigated whether molecular chaperones with a proven role in protein folding and belonging to the other two major families of stress proteins, i.e. Hsp60 or Hsp90, can substitute for Hsc70 [22].
• The dissociation constants of peptide P3a (the recognition sequence of clathrin light chain LCa by hsc70) and S peptide of ribonuclease for 60-kDa protein are 13 and 7 microM, respectively [1].

Analytical, diagnostic and therapeutic context of HSPA8

• We studied the process of disassembly by using cryo-electron microscopy to identify the initial binding site of Hsc70 on clathrin-C58J baskets at pH 6, under which conditions disassembly does not proceed further [23].
• Quantitative Northern blot analysis with strand-specific probes was used to demonstrate the Dex-inducible accumulation of hsc70 antisense RNA in proliferating cell cultures and the inhibition of hsc70 RNA levels [18].
• Conformational change of chaperone Hsc70 upon binding to a decapeptide: a circular dichroism study [24].
• Differential scanning calorimetry was used to monitor the thermal transitions of the 70 kDa heat shock cognate protein (Hsc70) [25].

References