Enzymes synthesized by hyperthermophiles (bacteria and archaea with optimal growth temperatures of >80°C), also called hyperthermophilic enzymes, are typically thermostable (i.e., resistant to irreversible inactivation at high temperatures) and are optimally active at high temperatures. These enzymes share the same catalytic mechanisms with their mesophilic counterparts. When cloned and expressed in mesophilic hosts, hyperthermophilic enzymes usually retain their thermal properties, indicating that these properties are genetically encoded. Sequence alignments, amino acid content comparisons, crystal structure comparisons, and mutagenesis experiments indicate that hyperthermophilic enzymes are, indeed, very similar to their mesophilic homologues. No single mechanism is responsible for the remarkable stability of hyperthermophilic enzymes. Increased thermostability must be found, instead, in a small number of highly specific alterations that often do not obey any obvious traffic rules. After briefly discussing the diversity of hyperthermophilic organisms, this review concentrates on the remarkable thermostability of their enzymes. The biochemical and molecular properties of hyperthermophilic enzymes are described. Mechanisms responsible for protein inactivation are reviewed. The molecular mechanisms involved in protein thermostabilization are discussed, including ion pairs, hydrogen bonds, hydrophobic interactions, disulfide bridges, packing, decrease of the entropy of unfolding, and intersubunit interactions. Finally, current uses and potential applications of thermophilic and hyperthermophilic enzymes as research reagents and as catalysts for industrial processes are described
Bio-based succinate is receiving increasing attention as a potential intermediary feedstock for replacing a large petrochemical-based bulk chemical market. The prospective economical and environmental benefits of a bio-based succinate industry have motivated research and development of succinate-producing organisms. Bio-based succinate is still faced with the challenge of becoming cost competitive against petrochemical-based alternatives. High succinate concentrations must be produced at high rates, with little or no by-products to most efficiently use substrates and to simplify purification procedures. Herein are described the current prospects for a bio-based succinate industry, with emphasis on specific bacteria that show the greatest promise for industrial succinate production. The succinate-producing characteristics and the metabolic pathway used by each bacterial species are described, and the advantages and disadvantages of each bacterial system are discussed.
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