Thermotolerant desert lizards characteristically differ in terms of heat-shock system regulation.

We compare the properties and activation of heat-shock transcription factor (HSF1) and the synthesis of a major family of heat-shock proteins (HSP70) in lizard species inhabiting ecological niches with strikingly different thermal parameters. Under normal non-heat-shock conditions, all desert-dwelling lizard species studied so far differ from a northern, non-desert species (Lacerta vivipara) in the electrophoretic mobility and content of proteins constitutively bound to the regulatory heat-shock elements in the heat-shock gene promoter. Under these conditions, levels of activated HSF1 and of both HSP70 mRNA and protein are higher in the desert species than in the non-desert species. Upon heat shock, HSF1 aggregates in all species studied, although in desert species HSF1 subsequently disaggregates more rapidly. Cells of the northern species have a lower thermal threshold for HSP expression than those of the desert species, which correlates with the relatively low constitutive level of HSPs and high basal content of HSF1 in their cells.

Comparison of the heat shock response in ethnically and ecologically different human populations.

In response to heat shock or other metabolic insults, an increased expression of different heat shock proteins (hsps) and, in particular, members of the hsp70 family is observed in human cells. Using two-dimensional electrophoresis, we compared the pattern of hsp70 synthesis in human fibroblast cell lines isolated from two contrasting groups of individuals. The first group was represented by native Turk-men living in the hot desert of Middle Asia; the second group consisted of Russians living in moderate climatic regions of European Russia. This analysis has shown that fibroblasts isolated from Turkmen after severe heat shock exhibited intensive synthesis of all hsps in parallel with synthesis of many other cellular proteins, while only trace synthesis of hsps was observed in the second group (Russians). Surprisingly, Northern analysis of RNA synthesis failed to reveal any differences between the two groups after heat shock treatment. When survival of fibroblasts after severe heat shock treatment was assessed by colony formation assay, the cells of the first group exhibited significantly higher survival rates.

Heat shock proteins and thermoresistance in lizards.

The synthesis of heat shock proteins (hsps) at normal physiological and elevated temperatures has been correlated with the natural adaptation of an organism to heat in nine lizard species studied. These species differ drastically by their adaptation to elevated temperature and represent a spectrum of forms isolated from various geographical regions of the Union of Soviet Socialist Republics. The synthesis of hsps belonging to the hsp70 family and their correspondent mRNAs have been compared at different temperature regimes. This analysis has shown that lizards inhabiting the Middle Asia deserts are characterized by a higher content of hsp70-like proteins at normal physiological temperatures (2- to 5-fold differences) when compared with the forms from central and northern regions of the European part of the Union of Soviet Socialistic Republics. Analysis of hsp70 mRNA at different temperatures substantiated these observations, showing evident correlation between adaptation of a given form to hyperthermia and the quantity of hsp70 mRNA in the cells under non-heat-shock conditions. The results obtained with a wide spectrum of ecologically different lizard species, coupled with other relevant data, enable us to propose a general rule applicable to poikilothermic organisms. This rule postulates the direct correlation between the characteristic temperature of the ecological niche of a given species and the amount of hsp70-like proteins in the cells at normal temperature.

The autophosphorylation reaction in the mechanism of activation of pig brain cyclic AMP-dependent protein kinase.

Autophosphorylation of cyclic AMP-dependent protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) was shown to occur via an intramolecular mechanism: the regulatory subunit undergoes phosphorylation only within the holoenzyme. The phospho form of the catalytic subunit has the capacity to phosphorylate the regulatory subunit. The phosphotransferase reaction and the reaction of autophosphorylation were found to proceed with the involvement of the same active site. The activation constant of phospho- and dephosphoprotein kinase under the influence of cyclic AMP and the dissociation constant of the cyclic AMP complex with phospho- and dephospho forms of the holoenzyme were estimated. Autophosphorylation was demonstrated to lead to almost complete dissociation of the holoenzyme under the influence of cyclic AMP. Circular dichroism spectra of the phosphorylated and non-phosphorylated forms of protein kinase were studied. The relative content of the secondary structure elements in proteins was estimated and conformational changes were detected in the enzyme upon its interaction with cycli AMP. The anti-conformation of the cyclic nucleotide fixed in the complex with the phospho form of the regulatory subunit is suggested.