70-kDa Heat Shock Cognate Protein Research Articles

Overexpression in Escherichia coli, purification and characterization of the molecular chaperone HSC70

The 70-kDa heat-shock cognate protein (HSC70), a constitutively expressed protein in mammalian cells, plays a major role in several cellular processes such as protein folding and assembly, uncoating of clathrin-coated vesicles and transport of protein through membranes. HSC70 has been overexpressed in Escherichia coli in a soluble form using a designed two-cistron expression vector, and purified to homogeneity in a two-step procedure involving ion-exchange and affinity chromatography. Up to 20 mg of pure protein could be obtained from 11 of cell culture. Amino-terminal sequencing of the recombinant protein gives the expected sequence, and non-denaturing gel electrophoresis as well as gel filtration analysis reveal the presence of self-associating species that could be dissociated by ATP. Crosslinking studies confirm the presence of multiple species and the dissociating effect of ATP. Temperatures above 42 degrees C induce the aggregation of HSC70; ATP shifts this effect to higher temperatures. The recombinant protein displays a low intrinsic ATPase activity that can be stimulated about threefold by binding to apocytochrome c, a permanently unfolded protein, while native cytochrome c has no effect on the ATPase activity indicating that recombinant HSC70 binds specifically unfolded protein but not their native counterpart. Thus, efficient production of recombinant HSC70 having structural and functional properties comparable to those of the natural protein could be achieved, thereby allowing the molecular basis of the chaperone function and its regulation through ATP hydrolysis to be probed.

Interaction of 70-kDA heat shock cognate protein with peptides and myo-inositol monophosphatase.

Fluorescence techniques have been used to investigate the interaction of bovine 70-kDa heat shock cognate protein (Hsc 70) with small molecular weight peptides and myo-inositol monophosphatase. The emission properties of Hsc 70 remain invariant upon addition of ATP. The results of steady-state fluorescence indicate that the tryptophan residues of Hsc 70 are exposed to the rapidly relaxing aqueous solvent. Binding of residues 1-20 of ribonuclease A (RNase S-peptide) to Hsc 70 causes protein fluorescence quenching which was used to determine a dissociation constant Kd = 2.7 microM for the binary Hsc 70.RNase S-peptide complex. The octapeptide corresponding to the NH2-terminal portion of sickle cell hemoglobin recognizes Hsc 70 and binds with a Kd = 9.3 microM. Binding of RNase S-peptide to Hsc 70 produces a small enhancement of ATPase activity. Unfolded myo-inositol monophosphatase, tagged with the fluorescent probe 5-[2-(2-iodoacetamido)ethylamino]-1-naphthalenesulfonic acid, recognizes Hsc 70; the formation of a stable complex was detected by steady-state emission anisotropy measurements. The rate and extent of recovery of catalytic activity of unfolded myo-inositol monophosphatase is not influenced by Hsc 70. It is suggested that interaction of Hsc 70 with unfolded proteins in the cell may be able to delay the formation of misfolded structures.

70 kDa heat shock cognate protein is a transformation-associated antigen and a possible target for the host's anti-tumor immunity.

We previously investigated a novel heat-inducible transformation-associated cell surface Ag that is expressed on the activated H-ras oncogene-transformed rat fibrosarcoma W31, but not its parental nontransformed fibroblast WFB. This Ag was detected by mAb 067. Herein, we characterized the molecular nature of the Ag by using anti-heat shock protein (HSP) mAb. The accumulated data indicated that the cell surface expression of Ag was clearly enhanced by several stressors, such as TNF, L-azetidine-2-carboxylic acid, and sodium arsenite. The immunoprecipitate made with mAb 067 and W31 cell lysates reacted with anti-rat 70 kDa heat shock cognate (HSC) mAb, TG5E, indicating that 067-defined Ag may be a rat 70 kDa HSC. Because this Ag seemed to be one of the transformation-associated Ag of WFB, we further studied whether it could play an important role in the host's anti-tumor immunity. Peripheral T cells of rats primed with live BCG showed cytotoxicity to W31 but not to WFB. Because the possibility existed that HSP may interact with certain populations of T cells, we focused on the reactivity of CD4-CD8- double negative T (DNT) cells against 067-defined molecule. DNT cells from spleen and PBL of live BCG-primed rats showed the cytotoxicity against W31 cells. This cytotoxicity was completely blocked by mAb 067 and anti-CD3 mAb. However, it was not blocked by mAb R48B1 and 109, which detect the MHC class I nonpolymorphic determinant and a target molecule of the cytolysis by poly I:C-induced NK cells, respectively. Furthermore, brefeldin A was able to block the cytotoxicity against W31 targets by DNT cells, but not by NK cells. These data suggest that 70 kDa HSC may be a tumor Ag and may act as a presenting molecule perhaps complexed with cellular peptides to certain DNT cells.

Aginactin, an agonist-regulated F-actin capping activity is associated with an Hsc70 in Dictyostelium.

We have previously isolated an agonist-regulated actin filament capping activity, called aginactin, that is associated with a 70-kDa protein (Sauterer, R. A., Eddy, R. J., Hall, A. L., and Coneelis, J. S. (1991) J. Biol. Chem. 266, 24533-24539). A 2.0-kilobase clone isolated from a Dictyostelium lambda gt11 cDNA library screened with affinity-purified aginactin antibodies displays an overall sequence identity of 73% to the 70-kDa heat shock cognate protein, Hsc70, from various species. Aginactin capping activity and the 70-kDa protein bind to ATP-agarose columns and are quantitatively depleted from the load, indicating that an Hsc70 is associated with aginactin activity. Moderate stringency Southern blots indicate the presence of no fewer than six Hsc70-related sequences. Immunofluorescent staining of vegetative Dictyostelium AX3 cells with aginactin antibodies reveals a colocalization of aginactin-associated Hsc70 in F-actin-rich regions of the cell cortex and cell protrusions. Nuclei and organelles lacked positive staining indicating that the aginactin-associated Hsc70 is cytosolic. The levels of cytoskeletal-associated Hsc70 correlate with the loss of barbed end capping activity following cAMP stimulation, suggesting that the uncapping of barbed filament ends through an Hsc70-associated process may account for the increase in nucleation activity observed at 5 s following agonist stimulation.

Demonstration of selective protein complexes of p53 with 73 kDa heat shock cognate protein, but not with 72 kDa heat shock protein in human tumor cells

It has been demonstrated that p53, especially, mutant p53 (mp53), makes protein complexes with major heat shock proteins hsp72/hsc73. However, there is no direct evidence showing whether hsp72 or hsc73 could bind preferentially to p53. In the present study, using TYKnu human ovarial carcinoma cells and monoclonal antibodies reacting specifically to hsp72/hsc73, we were able to find the selective protein complex formation with p53, presumably mp53, and hsc73, but not in the case of p53 and hsp72. The p53-hsc73 protein complexes dissociate with the addition of ATP, indicating that the dissociation is dependent upon the ATP-hydrolysis. These data suggest that hsc73 rather than hsp72 plays an important role in the yet undefined mechanism of disregulated cell growth control by mp53.

Three-dimensional structural resemblance between the ribonuclease H and connection domains of HIV reverse transcriptase and the ATPase fold revealed using graph theoretical techniques

Using 3D searching techniques based on algorithms derived from graph theory, we have established two previously unreported structural similarities involving the ribonuclease H (RNase H) domain of HIV-1 reverse transcriptase (RT). First, we report that there is a strong similarity between the 3D folds of the RNase H domain of RT and the ‘ATPase folds’ of hexokinase, the 70 kDa heat-shock cognate protein and actin. Like RNase H, these enzymes are involved in nucleotide binding and metal ion-catalysed cleavage of a phosphodiester bond. Similarities of the folding motif and the position of the metal-binding site in these enzymes suggest possible functional analogies and evolutionary relationships with RNase H. Second, we find there is a strong resemblance between the folds of the RNase H domain and of the p66 and p51 ‘connection’ domains of RT. It is possible that this striking similarity within the RT structure indicates a possible ancestral gene doubling event. The similarity may also indicate that the connection domains possess functional roles in addition to those previously suggested, and they may therefore represent a further target for the design of therapeutic agents.

70-kDa Heat-Shock Cognate Protein Colocalizes with Karyophilic Proteins into the Nucleus during Their Transport in Vitro

Recently, we showed that antibodies against 70-kDa heat-shock cognate protein (hsc70) inhibit nuclear transport of karyophilic proteins in vivo. In this study, we examined the involvement of hsc70 in nuclear transport using a digitonin-permeabilized cell-free transport system. Depletion of the cytosolic extract required for nuclear transport of hsc70 by incubation with anti-hsc70 antibodies reduced the nuclear transport activity significantly, and addition of purified hsc70 to the depleted extract restored the transport activity. We examined the localization of hsc70 during nuclear transport in vitro by indirect immunofluorescence studies. Hsc70 accumulated in the nucleus when bovine serum albumin (BSA) conjugated to SV40 large T-antigen nuclear localization signal (NLS) peptides (T-BSA) or nucleoplasmin was added exogenously to the cytosolic extract, but not when BSA conjugated to transport-incompetent point-mutated NLS peptide was added. This karyophilic protein-dependent accumulation of hsc70 was dependent on the cytosolic extract, temperature, and ATP and was sensitive to wheat germ agglutinin. Addition of excess unlabeled T-BSA to the cytosolic extract competitively inhibited the nuclear accumulation of fluorescently labeled T-BSA or nucleoplasmin, but did not affect accumulation of hsc70 into the nucleus. These results show that hsc70 is required for nuclear transport and that it is colocalized with karyophilic proteins during their active import into the nucleus in vitro.

Conformational change of chaperone Hsc70 upon binding to a decapeptide: a circular dichroism study.

The conformation of bovine Hsc70, a 70-kDa heat shock cognate protein, and its conformational change upon binding to decapeptides, was studied by CD spectroscopy and secondary structure prediction (Chou, P.Y. & Fasman, G.D., 1974, Biochemistry 13, 222-245). The CD spectra were analyzed by the LINCOMB method, as well as by the convex constraint analysis (CCA) method (Perczel, A., Park, K., & Fasman, G.D., 1992, Anal. Biochem. 203, 83-93). The result of the CD analysis of Hsc70 (15% alpha-helix, 24% beta-sheet, 24% beta-turn, and 38% remainder) was very similar to the predicted secondary structure for the beta-sheet (24%) and the beta-turn (29%). However, there is disagreement between the alpha-helical content by CD analysis (15%) and the predicted structure (30%). In spite of the fact that the decapeptides contained a considerable amount of beta-sheet (22%), the interaction of the heat shock protein with the peptide resulted in an overall decrease in the content of beta-sheet conformation (-15%) of the complex. This may be due to induction of a molten globule state. The result of the CCA analysis indicated that the Hsc70 undergoes a conformational change upon binding the decapeptides.

Effect of polyanions on the refolding of human acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF) is unstable at physiological temperatures in the absence of polyanions such as heparin. Therefore, the effect of temperature on the kinetics of refolding of aFGF has been examined in the presence and absence of several polyanions. The protein folds into its native state at temperatures up to 30 degrees C without polyanions with an activation energy of approximately 14 kcal/mol, but does not acquire native structure above this temperature. When heparin, inositol hexasulfate, or sulfate ion are present, aFGF refolds below 30 degrees C with a slightly reduced activation energy (10-11 kcal/mol). In addition, the protein now also renatures between 30 and 50 degrees C with activation energies of 1-2 (heparin), 16 (inositol hexasulfate), and 7 (sulfate) kcal/mol. Trace heavy metals appear to inhibit the refolding process, but a molecular chaperone (bovine 70-kDa heat shock cognate protein) and a peptidylprolyl isomerase (the FK506-binding protein) have no effect. It is concluded that the rate of refolding of aFGF at physiological temperatures is probably controlled by the interaction of a native-like state of the protein with an unknown polyanionic species.

Similarity of the three-dimensional structures of actin and the ATPase fragment of a 70-kDa heat shock cognate protein.

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. The alpha-carbon positions of 241 pairs of amino acid residues that are structurally equivalent within the two proteins can be superimposed with a root-mean-square difference in distance of 2.3 A; of these, 39 residues are identical, and 56 are conservative substitutions. In addition, the conformations of ADP are very similar in both proteins. A local sequence "fingerprint," which may be diagnostic of the adenine nucleotide beta-phosphate-binding pocket, has been derived. The fingerprint identifies members of the glycerol kinase family as candidates likely to have a similar structure in their nucleotide-binding domains. The structural differences between the two molecules mainly occur in loop regions of actin known to be involved in interactions with other monomers in the actin filament or in the binding of myosin; the corresponding regions in heat shock proteins may have functions that are as yet undetermined. Placing the Ca2+ ATP of actin on the ATPase fragment structure suggests Asp-206 (corresponding to His-161 of actin) as a candidate proton acceptor for the ATPase reaction.

Secondary structure of the mammalian 70-kilodalton heat shock cognate protein analyzed by circular dichroism spectroscopy and secondary structure prediction

Heat shock proteins are rapidly synthesized when cells are exposed to stressful agents that cause protein damage. The 70-kDa heat shock induced proteins and their closely related constitutively expressed cognate proteins bind to unfolded and aberrant polypeptides and to hydrophilic peptides. The structural features of the 70-kDa heat shock proteins that confer the ability to associate with diverse polypeptides are unknown. In this study, we have used circular dichroism (CD) spectroscopy and secondary structure prediction to analyze the secondary structure of the mammalian 70-kDa heat shock cognate protein (hsc 70). The far-ultraviolet CD spectrum of hsc 70 indicates a large fraction of alpha-helix in the protein and resembles the spectra one obtains from proteins of the alpha/beta structural class. Analysis of the CD spectra with deconvolution methods yielded estimates of secondary structure content. The results indicate about 40% alpha-helix and 20% aperiodic structure within hsc 70 and between 16-41% beta-sheet and 21-0% beta-turn. The Garnier-Osguthorpe-Robson method of secondary structure prediction was applied to the rat hsc 70 amino acid sequence. The predicted estimates of alpha-helix and aperiodic structure closely matched the values derived from the CD analysis, whereas the predicted estimates of beta-sheet and beta-turn were midway between the CD-derived values. Present evidence suggests that the polypeptide ligand binding domain of the 70-kDa heat shock protein resides within the C-terminal 160 amino acids [Milarski, K. L., & Morimoto, R. I. (1989) J. Cell Biol. 109, 1947-1962].(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterisation of a Leishmania donovani antigen belonging to the 70‐kDa heat‐shock protein family

A Leishmania donovani promastigote cDNA library was screened with serum obtained from a patient infected with visceral leishmaniasis. Sequence analysis of a clone obtained from this library revealed that the 600-bp insert corresponded to the carboxy-terminal region of an antigen related to the 70-kDa heat-shock protein family. The full-length sequence of the corresponding gene (1959 nucleotides) was determined after isolation of genomic clones. Genes encoding the antigen are present on a single chromosome as a series of approximately twelve 3.7-kb direct tandem repeats. The antigen can be identified as a 70-kDa heat-shock cognate protein by virtue of its molecular mass, sequence and constitutive expression during heat shock. It is expressed at all stages of the parasite life-cycle. Antibodies against the lambda gt11 fusion protein were detected in more than 50% of serum samples obtained from patients with visceral leishmaniasis, but were not detected in sera from patients with cutaneous leishmaniasis or Chagas' disease.

β-internexin is a microtubule-associated protein identical to the 70-kDa heat-shock cognate protein and the clathrin uncoating ATPase

Abstract We have examined the relationship of the ubiquitous 68-70-kDa cytoskeletal-associated protein beta-internexin (Napolitano, E. W., Pachter, J. S., Chin, S. S. M., and Liem, R. K. H. (1985) J. Cell Biol. 101, 1323-1331) to heat-shock cognate 70 (hsc70), the major constitutive member of the mammalian heat-shock protein 70 (hsp70) family of stress proteins. We purify beta-internexin from rat brain microtubules and confirm its identity with hsc70 and the clathrin-uncoating ATPase by the following criteria: 1) The partial sequence of a cyanogen bromide-derived peptide from beta-internexin matches the inferred amino acid sequence of the cDNA clone pRC62 encoding hsc70 from rat brain (O'Malley, K., Mauron, A., Barchas, J. D., and Kedes, L. (1985) Mol. Cell. Biol. 5, 3476-3483). 2) Mixing experiments followed by two-dimensional gel analyses reveal the precise co-migration of beta-internexin, the clathrin-uncoating ATPase, and the in vitro translation product of cDNA clone pHSP-4 encoding rat brain hsc70. 3) beta-Internexin is recognized by a monoclonal antibody reactive against the class of hsp70 proteins. 4) beta-Internexin purified from a microtubule-associated protein-enriched fraction of rat brain by virtue of high affinity binding to ATP-agarose possesses clathrin cage-specific ATPase activity.

Heat-shock cognate protein (hsc71) and related proteins in mouse spermatogenic cells.

A monoclonal antibody (13D3) has been developed that recognizes a 71 kilodalton (71 kDa) protein on two-dimensional immunoblots of proteins extracted from a mixture of mouse spermatogenic cells (mainly pachytene spermatocytes and spermatids). This protein was shown by immunoblotting and adenosine triphosphate (ATP)-binding characteristics to be identical to a 71 kDa mouse heat-shock cognate (hsc) protein, hsc71, present in 3T3 cells. Along with a 70 kDa heat-shock inducible protein (hsp70), and a 74 kDa heat-shock cognate protein (hsc74), hsc71 is a product of the mouse HSP70 multigene family. Although antibody 13D3 reacted strongly with hsc71, it reacted only faintly with hsp70 in 3T3 cells, and not at all with hsc74 or a germ cell-specific hsp70-like protein (P70) on immunoblots of mixed germ cells. Antibody 13D3 is unique among known antibodies in its pattern of reaction with these heat-shock proteins. In immunofluorescence studies on isolated germ cells, 13D3 reacted uniformly with the cytoplasm of pachytene spermatocytes, round spermatids, and residual bodies, but only with the midpiece of spermatozoa. Antibody 13D3 recognizes other proteins in addition to hsc71 on two-dimensional immunoblots of condensing spermatids and spermatozoa. Two of the proteins (70 kDa/pI 6.4 and 70 kDa/pI 6.5) were present in condensing spermatids and spermatozoa, and another protein (69 kDa/pI 7.0) was detected only in spermatozoa. The new proteins also were recognized by monoclonal antibody 7.10, which reacts specifically with hsp70, hsc71, hsc74, and P70. Although [35S]methionine was incorporated into the new proteins in condensing spermatids, hsc71, hsc74, and P70 were not labeled. These results suggest that unique heat-shock proteins are synthesized late in spermatogenesis.

Lack of heat-shock response in preovulatory mouse oocytes

The response to heat (hs response) of preovulatory mouse oocytes was compared with that of mouse granulosa cells and characterized in regard to in vitro resumption of meiosis, amino acid incorporation into total protein, and qualitative analysis of protein synthesized before and after the shock. Granulosa cells displayed a hs response typical of other mammalian systems. When incubated at 43°C for 20–40 min, these cells maintained a normal level of amino acid incorporation into total protein, responded to stress by new synthesis of 33- and 68-kDa heat-shock proteins (hsps), and enhanced synthesis of 70-kDa heat-shock cognate protein (hsc70) and of 89- and 110-kDa hsps. In contrast to granulosa cells, preovulatory mouse oocytes were very sensitive to hyperthermia. Incubation at 43°C for 20–40 min strongly inhibited oocyte resumption of meiosis and protein synthesis and did not induce a new or enhanced synthesis of hsps. Unstressed preovulatory mouse oocytes constitutively synthesized 70- and 89-kDa polypeptides resembling hsc70 and hsp89 of granulosa cells.