Latest Research on Shock Proteins : Jun 2020

Small heat shock proteins are molecular chaperones.

Small heat shock proteins (sHsp) with a molecular mass of 15-30 kDa are ubiquitous and conserved. Up to now their function has remained enigmatic. Increased expression under heat shock conditions and their protective effect on cell viability at elevated temperatures suggest that they may have a function in the formation or maintenance of the native conformation of cytosolic proteins. To test this hypothesis we studied the influence of murine Hsp25, human Hsp27, and bovine alpha-B-crystallin (an eye lens protein homologous to sHsps) on the unfolding and refolding of citrate synthase and alpha-glucosidase in vitro. Here we show that all sHsps investigated act as molecular chaperones in these folding reactions. At stoichiometric amounts they maximally prevent the aggregation of citrate synthase and alpha-glucosidase under heat shock conditions and stabilize the proteins. Furthermore, they promote the functional refolding of these proteins after urea denaturation similar to GroE and Hsp90. The interaction both with unfolding and refolding proteins seems to be ATP-independent. [1]

Heat shock proteins and the immune response

Heat shock proteins (HSPs) or stress proteins are produced by prokaryotic and eukaryotic cells in response to a variety of insults. After this original definition, it has become increasingly clear that HSPs can modify the function and destiny of other proteins and thus play an important role in numerous physiological processes. The heat shock response is one of the most universal reactions known and HSPs are among the most conserved molecules in phylogeny. Here Stefan H.E. Kaufmann discusses the role of HSPs in immunity with respect to both their function and their antigenicity. [2]

Heat shock proteins: facts, thoughts, and dreams.

The most primitive mechanism of cellular protection involves the expression of a polypeptide family named heat shock or stress proteins (hsps). Some of these hsps are present in unstressed cells and play an important role in the folding and translocation of polypeptides across membranes. Thus, they have been termed molecular chaperones. Hsps are expressed in response to an array of stresses, including hyperthermia, oxygen radicals, heavy metals, ethanol, and amino acid analogues. In addition, the heat shock response is induced during clinically relevant situations such as ischemia/reperfusion and circulatory and hemorrhagic shock. All of the above stresses have in common that they disturb the tertiary structure of proteins and have adverse effects on cellular metabolism. Pretreatment of cells with a mild stress, sufficient to induce the expression of hsps, results in protection to subsequent insults. This phenomenon has been coined “stress tolerance” and is apparently caused by the resolubilization of proteins that were denatured during the stress. In addition, cellular structures (microfilaments and centrosomes) and processes (transcription, splicing, and translation) are stabilized or repaired during a second stress in stress tolerant cells and organisms. There is a great body of evidence indicating a direct role of hsps in the stabilization of these events. The intrinsic capacity of hsps to protect cells has potential relevance as a natural mechanism of organ protection during harmful environmental conditions and operative procedures, and in the combat against pathogens. [3]

Differential Expression Pattern of Heat Shock Protein Genes in Toxigenic and Atoxigenic Isolate of Aspergillus flavus

Aflatoxin biosynthesis in Aspergillus flavus requires coordinated expression of regulatory and structural genes. Aflatoxin production is optimum at 24-30°C and inhibition occurs at temperature higher than 35°C. Chaperones or heat-sock proteins are involved in processing of cellular protein and heat-stress induced protein, hence, we studied the genes encoding for heat-shock proteins under the influence of temperature (30°C vs. 37°C). A. flavus isolates, aflatoxigenic (MTCC9367) and atoxigenic (MTCC11580) were grown in glucose minimal salt broth for 24 hours for expression profile of selected genes using quantitative real-time PCR. We monitored the expression profile of genes encoding for heat-shock proteins (hsp98, hsp90, hsp70 and hsp60) and regulatory gene of aflatoxin biosynthesis pathway aflR. We found the similar trend for heat-shock proteins gene expression except hsp70 in aflatoxigenic and atoxigenic isolates of A. flavus. Expression for hsp70 was found to be upregulated at 30°C (vs 37°C)in atoxigenic isolate (P<0.001) of A. flavus in comparison of toxigenic (P<0.05) isolate. Since, heat-shock proteins are involved in protein folding and conformational stability of cellular proteins to maintain the biological activity, our data on transcripts encoding for heat-shock proteins suggested it may influence the aflatoxin biosynthesis process in A. flavus. [4]

Heat Shock Proteins in Cassia Species

Aim: Abiotic stresses, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress, are serious threats to plants. Heat shock proteins can assist in protein refolding under stress conditions at molecular levels. The proposed study was aimed to analyze and characterize the heat shock proteins at the molecular level in the Cassia species.

Study Design: The experiments designed were intended to study and characterize the heat shock proteins in the Cassia species using molecular approach.

Methodology: The samples were subjected to the varying heat treatments (30⁰C, 37⁰C and 42⁰C), and the proteins obtained were further sequenced for similarity search. The peptide sequence was synthesized chemically and conjugated with Keyhole limpet hemocyanin (KLH) for the production of antibodies. Western blot was carried out with the polyclonal antibodies to confirm the results.

Results: The gel analysis revealed a clearly visible over-expressed band at the highest induced temperature (42ºC) depicting the presence of a heat shock response in Cassia. BLASTp search of the peptide sequences obtained from trypsin digestion followed by LC-MS resulted in 14 hits, out of which one of the peptide was similar to a known HSP, thioredoxin peroxidase from Nicotiana tabacum. Rabbit polyclonal antibodies were synthesized against the KLH-tagged peptide. The Western blot confirmed binding of probes to the heat shock band observed for the temperature treatment at 42ºC. [5]

Reference

[1]  Jakob, U., Gaestel, M., Engel, K. and Buchner, J., 1993. Small heat shock proteins are molecular chaperones. Journal of Biological Chemistry, 268(3), pp.1517-1520.

[2] Kaufmann, S.H., 1990. Heat shock proteins and the immune response. Immunology today, 11, pp.129-136.

[3] De, A.M., 1999. Heat shock proteins: facts, thoughts, and dreams. Shock (Augusta, Ga.), 11(1), pp.1-12.

[4] Thakur, R., Tiwari, S. and Shankar, J., 2016. Differential expression pattern of heat shock protein genes in toxigenic and atoxigenic isolate of Aspergillus flavus. Microbiology Research Journal International, pp.1-9.

[5] Pant, G., Kumari Chauhan, U., Malla, S., Banupriya, S. and Pati, R. (2017) “Heat Shock Proteins in Cassia Species”, Biotechnology Journal International, 17(4), pp. 1-10. doi: 10.9734/BJI/2017/31006.

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