Cold-shock protein

Both the heat and cold shock response are universal and have been studied extensively. The major heat shock proteins (HSPs) are highly conserved. They are involved in the homeostatic adaptation of cells to harsh environmental conditions. Some act as molecular chaperones for protein folding, while others are involved in the processing of denatured polypeptides whose accumulation would be deleterious. The cold shock results in the transient induction of cold shock proteins (CSPs), which include a family of small acidic proteins carrying the cold shock domain. The CSPs appear to be involved in various cellular functions such as transcription, translation and DNA recombination. 

Major E. coli Cold Shock Proteins and Their Function... 

What could be the signal for the induction of the cold shock proteins It has been observed that shifting E. coli cells from 37 to 5 °C results in an accumulation of 70S monosomes with a concomitant decrease in the number of polysomes [129]. Further, it has been shown that a cold shock response is induced when ribosomal function is inhibited, e.g. by cold-sensitive ribosomal mutations [121] or by certain antibiotics such as chloramphenicol [94]. These data indicate that the physiological signal for the induction of the cold shock response is inhibition of translation caused by the abrupt shift to lower temperature. Then, the cold shock proteins RbfA, CsdA and IF2 associate with the 70S ribosomes to convert the cold-sensitive nontranslatable ribosomes into cold-resistant translatable ribosomes. This in turn results in an increase in cellular protein synthesis and growth of the cells. 

In contrast to most mRNAs, which become untranslatable after a temperature downshock, cold shock mRNAs possess a mechanism to form the translation initiation complex at low temperature without cold shock ribosomes. A close inspection of the mRNAs of class I cold shock proteins reveal that they are equipped with an extra ribosome-binding site called the downstream box located within the coding region of their transcript [130]. It would be interesting to know whether introduction of this downstream box into a cellular mRNA would convert it into a transcript which can be transcribed immediately after a cold shock. In the case of the cspA mRNA it has been shown that in the absence of the downstream box the initiation complex cannot be formed at low temperature during the accHmation phase [131]. 

Figure 13.11 Partial 9.4 T MALDI-FTMS spectrum of E. coli JM109, showing expression of cold shock protein.

Goldstein, S. Pelitt, S. N. Inouye, M. Major cold shock protein of Escherichia coli. Proc. Nat. Acad. Sci. USA 1990, 87, 283-287. 

Cold-shock proteins (Csps) are transiently expressed at a higher level in bacteria as a response to an abrupt decrease from normal physiological temperature. Their exact biological function is still unknown, but translational regulation, possibly via RNA chaperoning, has been discussed. " Csps from mesophiles and thermophiles differ widely in their stability, but show... 

Fig. 4. Stereoviews of TmCsp. (A) Stereoview of a superposition of the backbone atoms of the 21 accepted structures of TmCsp. (B) Stereoview of a representative ribbon diagram of TmCsp. The secondary-structure elements are indicated. (C) Stereoview of the solution NMR structure of TmCsp (rotated ribbon diagram). Location of a possible peripheral ion cluster. Reprinted from Eur. J. Biochem., Vol. 268, W. Kremer, B. Schuler, S. Harrieder, M. Geyer, W. Gronwald, C. Welker, R. Jaenicke and H. R. Kalbitzer, Solution NMR structure of the cold-shock protein from the hyperthermo-philic bacterium Thermotoga maritima , pp. 2527-2539, Copyright 2001, with permission from Blackwell Science.

The fastest-folding small proteins generally fold on much slower time scales than the time scale of formation of secondary structure. The speed record is currently held by lambda(6-85), a truncated, monomeric form of the N-terminal domain of lambda repressor, which refolds with a half-life of approximately 140 fjis. A thermostable lambda(6-85) variant with alanine substituted for glycine residues 46 and 48 in the third helix folds faster in dilute solutions of de-naturant, with an extrapolated half-life of less than 10 /us in water.13 Cold-shock protein CspB from Bacillus subtilis folds in about 1 ms.61 Engineered mutants of the P22 Arc repressor62 and CI263 fold in a fraction of a millisecond. 

Figure 7.15. Functions of cold-shock proteins (Csp s) as RNA chaperones. The model shows how Csp s assist in coupling transcription to translation. Cold-shock proteins bind relatively weakly to nascent mRNA extending from the RNA polymerase complex (RNAP) and maintain the mRNA in a linear form that can be bound to ribosomes and translated into protein. Under nonstressful conditions, the weakly binding Csp s are present at adequate concentrations to perform this chaperoning function. However, during cold stress, the propensity for RNA to form secondary structures that block translation becomes greater. This necessitates that a higher level of Csp s be present in the cell, to ensure that chaperoning of mRNA is effective. (Figure modified after Graumann and Marahiel, 1998.)...

Jiang, W., Y. Hou, and M. Inouye (1997). CspA, the major cold-shock protein of Escherichia coli, is an RNA chaperone. J. Biol. Chem. 272 196-202. 

A group of proteins that are synthesized by plant cells, prokaryotic cells, and eukaryotic cells in response to cold stress. It has been suggested that cold-shock proteins (CSPs) function as chaperones for mRNA. See Graumann, P.L. and Marshiel, M. A., A superfamily of proteins that contain the cold-shock domain, Trends Biochem. Sci. 23,286-290,1998 Phadtare,... 

Alsina, J., and Inouye, M., Cold-shock response and cold-shock proteins, Curr. Opin. Microbiol. 2, 175-180, 1999 Sommerville, J., Activities of cold-shock domain proteins in translational control, Bioessays 21, 319-325,1999 Graumann, P.L. andMarahiel, M.A., Cold shock response in Bacillus subtilis, J. Mol. Microbiol. Biotechnol. 1, 203-209, 1999 Loa, D.A. and Murata, N., Responses to cold shock in cyanobacteria, J. Mol. Microbiol. Biotechnol. 1, 221-230,1999 Ermolenko, D.N. and Makhatadze,... 

D. Perl, C. Welker, T. Schindler et al. Conservation of rapid two-state folding in mesophiUc, thermophilic and hyperthermophilic cold shock proteins. Nature Structural Biology, 5 (1998), 229. 

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