[75]

A New Paradigm for Environmental Limits of Life: Finding Clues from Unknown Proteins.  J.D. Ng, R.C. Hughes, M. Byrnes, M. Davis and G. Podila. Dept. of Biological Sciences and Laboratory for Structural Biology.  University of Alabama in Huntsville, AL

   The evolution and acclimatization of life of an organism are eventually determined by the stability of the protein’s three-dimensional fold and their specificity.  Common topological shapes of proteins are observed in almost all known structure to-date. Recurring structural motifs in proteins may be a consequence of evolution or as prevalent folds that are inherently thermodynamically stable.  To investigate this phenomenon, we have examined the “hypothetical protein” structures from psychrophilic (cold-loving), hyperthermophilic (hot-loving) and mesophilic (moderate temperature) organisms and compared them to all known protein folds presently known.  Hypothetical proteins are gene products that have no identifiable function and exist as a significant fraction in all genomes. They are of particular interest because these proteins may contain ancient or undiscovered protein folds associated with new functions.  A structural genomics approach has been used in this investigation in which hypothetical proteins have been cloned from known genome sequences.  Recombinant protein expression systems were constructed where purified proteins were crystallized and their structures determined by X-ray crystallography. Comparing structures of homologous proteins from different domains and temperature tolerance of life uncovers the minimal structures important for survival in extreme environments.  Knowledge of the limits, chemical and physical requirements, and output of extremophilic life on Earth gives considerable insight into where life may now be found or have previously existed on other planets within our solar system.  These signatures can then be used to direct subsequent exploration of other planets.