Over the past 4 decades, our knowledge about life under extreme conditions has dramatically expanded. Organisms have been found that can function down to -25 °C (psychrophiles) and up to 122 °C (hyperthermophiles). Extremes pressure (piezophiles) can also be tolerated, as well as other stressors. Understanding extremophiles is important in its own right. It is also relevant for human health, biotechnological applications, and our search for life elsewhere in the universe.
The dynamics of proteins in these extremophiles is important. A popular theory says that extremophile proteins have adapted to maintain the same flexibility at their different optimal growth temperatures. is proposed to maintain ‘‘corresponding states’’ regarding flexibility. However, there have been relatively few quantitative tests of this theory, and some measurements seem to conflict with the hypothesis.
As one test of the ‘corresponding states’ hypothesis, we have investigated the ⁵⁷Fe dynamics of two distinct rubredoxins as a function of temperature. Rubredoxins (Rds) are the simplest Fe-S proteins; they have an Fe(S-cys)₄ center and have molecular masses on the order of 6 kDa. For this study we have compared Rds from the hyperthermophile Pyrococcus furiosus and the psychrotolerant organism Pseudomonas sp. strain AU10. P. furiosus is a marine archaebacter with an optimal growth temperature of ~100 °C. Pseudomonas sp. strain AU10 is an Antarctic freshwater organism with an optimal growth temperature of 28 °C that can still grow close to 0 °C. NRVS results from 40 to 340K will be presented and interpreted in light of recent molecular dynamics calculations, Mössbauer data, NMR studies, and variable temperature x-ray diffraction results.

Tzanko Doukov

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