Warm, Hot, and Very Hot

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Science  02 Jun 2000:
Vol. 288, Issue 5471, pp. 1551
DOI: 10.1126/science.288.5471.1551a

The accumulation of high-resolution three-dimensional structures of proteins offers the opportunity to practice comparative structural genomics. Szilágyi and Závodszky have tackled the question of how protein structure is stabilized as the temperature at which the organism lives increases from something we would be comfortable with to 100°C. After carefully selecting well-determined data sets, they began with a database of 93 structures of 25 proteins, 29 from thermophiles and 64 from mesophiles.

In general, the number of hydrogen bonds and secondary structural elements (α-helices and β-sheets) do not correlate with temperature, while ion pairs (salt bridges) do. By subdividing their thermophilic data into hot (45 to 80°C) and very hot (100°C), they were then able to uncover correlations of fewer cavities in the very hot and of greater polarity of exposed surface in the merely hot. This apparent demarcation also was reflected in the type of ion pairings observed, with an increase only in weaker bonds (as defined by separation distance) in the hot subgroup but increases in strong and weak ion pairs for the very hot. (Approximately 14 more weak salt bridges are expected for a protein in an organism growing at 80°C than for its counterpart in a mesophilic host.) A particularly interesting outcome of the subgrouping into hot and very hot, tempered by the caveat that only five structures comprise the latter, is the possibility that different evolutionary histories of these classes of organisms are responsible for the distinct strategies adopted for protein stabilization.—GJC

Structure8, 493 (2000).

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