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Mar 12, 2013

Survival on Mars Depends on Key Protein Features

  • In order for life to function on Mars and other extreme environments, proteins need to possess certain characteristics, according to researchers at the University of Maryland School of Medicine. The team studied organisms that survive in the extreme environment of Antarctica. They found subtle but significant differences between the core proteins in ordinary organisms and Haloarchaea, organisms that can tolerate severe conditions such as high salinity, desiccation, and extreme temperatures. The research gives scientists a window into how life could possibly adapt to exist on Mars.

    Haloarchaeal microbes contain proteins that are acidic, with their surface covered with negatively charged residues, the scientists discovered. Most ordinary organisms contain proteins that are neutral on average. The negative charges found in the unusual organisms keep proteins in solution and help to hold on tightly to water, reversing the effects of high salinity and desiccation, the team reports.

    In the current study, the scientists identified additional subtle changes in the proteins of one Haloarchaeal species named Halorubrum lacusprofundi. These microbes were isolated from Deep Lake, a very salty lake in Antarctica. They sequenced this microbe and compared to 12 Haloarchaea from temperate climates by comparative genomics. Amino acid substitutions for 604 H. lacusprofundi proteins belonging to conserved haloarchaeal orthologous groups were determined and found to occur at 7.85% of positions invariant in proteins from mesophilic Haloarchaea.

    The changes found in proteins from the halophilic organisms allow them to work in both cold and salty conditions, when temperatures may be well below the freezing point of pure water. Water stays in the liquid state under these conditions much like snow and ice melt on roads that have been salted in winter.

    “In such cold temperatures, the packing of atoms in proteins must be loosened slightly, allowing them to be more flexible and functional when ordinary proteins would be locked into inactive conformations,” says Shiladitya DasSarma, Ph.D., professor in the department of microbiology and immunology at the University of Maryland School of Medicine. “The surface of these proteins also have modifications that loosen the binding of the surrounding water molecules.

    “These kinds of adaptations are likely to allow microorganisms like Halorubrum lacusprofundi to survive not only in Antarctica, but elsewhere in the universe,” continues Dr. DasSarma. “For example, there have been recent reports of seasonal flows down the steep sides of craters on Mars, suggesting the presence of underground brine pools. Whether microorganisms actually exist in such environments is not yet known, but expeditions like NASA’s Curiosity rover are currently looking for signs of life on Mars.”

    The study was published online yesterday in the journal PLoS One, in a paper titled “Amino Acid Substitutions in Cold-Adapted Proteins from Halorubrum lacusprofundi, an Extremely Halophilic Microbe from Antarctica”.


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