Proteins in deep sea environment. A combined approach by computer simulation and neutron scattering.

Paolo Calligari, CBM-CNRS, Orleans, France

The adaptation to extreme environmental conditions of living organisms is one of the challenging areas in molecular biology. In the last decades particular interest has been devoted to organisms which populate the deep-sea near hydrothermal chimneys, where the temperature can change over small distances from 4°C up to ~100°C, and pressure usually reaches values of around 100 MPa. Here I present a study of the anti-association factor 6 (IF6) from the Archaeon Methanococcus Jannaschii, which lives at 2600m under sea-level at temperatures of around 80°C. This protein limits the rate of translation of DNA and has been proven to be sensitive to external stimuli and to the global status of the cell. It plays thus a fundamental role for the life of these bacteria. Very recent results from neutron scattering and molecular dynamics simulation on the influence of extreme conditions - pressures up to 1kbar and high temperatures - on the structure and dynamics of IF6, are used to compare the variants produced by Methanoccoccus Jannaschii and by Saccharomyces cerevisiae (Baker yeast), which lives under normal conditions. Quasielastic neutron scattering experiments have been undertaken to show that the dynamical behavior of both proteins in their .natural. and reciprocal .extreme. conditions is affected. We will interpret the dynamics of IF6 in the frame of the fractional Brownian dynamics (fBD) model, which has been proven to describe the internal dynamics of proteins very well over a large range of time scales from sub-nanoseconds to seconds. Moreover, we will show how the small structural differences between the two homologous proteins affect the global response of the proteins to their environmental conditions. These results will be used to discuss a new approach to studies on environmental effects and their relation to evolutionary adaptation of proteins.

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