Cold-induced proteins

Cold stress may induce synthesis of heat-shock (stress) proteins. Exposure of cells to cold shock may lead to the induction of one or more of the classes of molecular chaperones that also are induced by heat shock. This is strong evidence that low temperature, like high temperature, can lead to non-native protein structures in vivo and, therefore, to the requirement for enhanced chaperoning activity. Induction of cold-induced protein chaperones has been seen in bacteria (Salotra et al., 1995), in whole organism studies of ectothermic animals (Petersen et al., 1990 Yocum et ah, 1991),... 

Figure 3. Other regulated acylation reactions involved in E. coli lipid A biosynthesis under special conditions. The reactions catalyzed by LpxP (formerly known as Ddg) [59] and LpxY (also known as PagP or CrcA) [51] are shown. LpxP is a cold induced protein which incorporates an unsaturated 16 carbon fatty acyl chain in place of the laurate normally incorporated by HtrB. LpxY, the expression of which is activated by the PhoP/PhoQ system [51], is an outer membrane protein that incorporates palmitate to make hepta-acylated lipid A. LpxY is capable of acylating lipid X, lipid IVa, and lipid A, as well as Kdo2-lipid IVa (as shown). The physiological substrate is probably lipid A, given that LpxY is an outer membrane protein.

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. 

Fig. 29. Equilbrium unfolding of C40A/C82A/P27A (pseudo-wild-type) barstar monitored by A R, mean residue circular dichroism. Conditions for near-UV CD were 50 /xM protein in 50 mM Tris-HCl buffer, pH 8, 0.1 M KC1, path length 1 cm. (A) Urea-induced unfolding at 25°C at urea concentrations as indicated. (B) Cold-induced unfolding in...

The generality of the end-wise depolymerization kinetic model is indicated by the comparison of the observed and predicted time-courses of cold-induced microtubule disassembly (Fig. 3). See Self-Assembly Protein Polymerization... 

Figure 3. Progress curve for cold-induced depolymerization after chilling microtubules (assembled at 30°C using 2.1 mg/ml tubulin and 0.4 mg/ml microtubule-associated proteins). The data points are experimentally determined, and the solid line is based on the theoretical treatment -T...

Entrapping of bioactive ingredients by polymer matrix in gel or microgel particles heat-induced or cold-induced aggregation and gelation of globular proteins (microcapsules of 5-5000 pm)... 

In the case of cold-induced aggregation and gelation, two different types of gel microstructure, namely filamentous and particulate (Figure 2.1), have been obtained by adding different concentrations of a ferrous salt to solutions of pre-denatured p-lactoglobulin (the major whey protein). This substantial difference in microstructure turns out to have a major impact on the iron delivery, due to the different sensitivities of the structures to the relevant environmental conditions, such as pH and the presence of digestive enzymes. In particular, the filamentous gel micro-... 

Biochemistry and molecular biology of cold-inducible enzymes and proteins in higher plants... 

In those cases for which it was examined it was found that cold-induced changes in the polypeptide pattern can be accounted for by changes in translatable mRNA populations. Low temperature-induced changes in mRNA populations have been reported for a number of plant species using in vitro translation assays in combination with protein electrophoresis (Meza-Basso et al., 1986 Mohapatra et al., 1987a,b Gilmour et al., 1988 Cattivelli Bartels, 1989 LSng et al., 1989). 

Guy, C.L. Haskell, D. (1987). Induction of freezing tolerance in spinach is associated with the synthesis of cold acclimation induced proteins. Plant Physiology 84, 872-8. 

As mentioned earlier, proteins are subject to cold denaturation because they exhibit maximal stability at temperatures greater than 0°C. The basis of this effect is the reduction in the stabilizing influence of hydrophobic interactions as temperature is reduced. Recall that the burial of hydrophobic side-chains in the folded protein is favored by entropy considerations (AS is positive), but that the enthalpy change associated with these burials is unfavorable (AH, too, is positive). Thus, as temperature decreases, there is less energy available to remove water from around hydrophobic groups in contact with the solvent. Furthermore, as temperature is reduced, the term [— TAS] takes on a smaller absolute value. For these reasons, the contribution of the hydrophobic effect to the net free energy of stabilization of a protein is reduced at low temperatures, and cold-induced unfolding of proteins (cold denaturation) may occur. 

The discoveries of Csp s and trigger factor may represent the tip of a large iceberg. In view of the pervasive effects of low temperature on the structures of all classes of macromolecules, it is reasonable to conjecture that many more types of proteins will be discovered whose roles are to offset the effects of cold shock on the cell. Some of these molecules may be expressed constitutively and may be part of the normal machinery of the cell. For example, certain ribosomal proteins are thought to function as RNA chaperones, and if present in sufficient amounts, these proteins may allow the cell to cope with the effects of cold shock on the structures of certain classes of RNAs. In yeast, a constitutively expressed ribosomal protein has helicase activity, and mutation in the gene encoding the protein confers on the cells a cold-sensitive phenotype (Schmid and Linder, 1992). Perhaps the apparent absence of cold-induced RNA chaperones in eukaryotic cells is... 

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