ABSTRACT
Thermophilic proteins or enzymes previously identified are stable inorganic solutions and heavy metals, and, under radiation as well as high temperatures, make them suitable for industrial applications. However, in some cases, enzymatic activities of thermophilic archae a showed lower activities than the mesophilic ones. It was, therefore, attempted to increase the stability of mesophilic enzymes or the enzymatic activities of thermophilic enzymes, showing that artificial increasing of natural enzyme’s stability from mesophilic microorganisms is difficult. Recently, artificial increasing of thermophilic archaeal enzyme’s activity was succeeded. In this chapter, successful examples for increasing of the enzymatic activities of two thermophilic archaeal enzymes are summarized. The ST0452 protein was identified from a acidothermophilic crenarchaeon, Sulfolobustokodaiias a bifunctional thermostable protein with multiple sugar-1-phosphate nucleotidylyltransferase and amino-sugar-1-phosphate acetyl transferase activities, which were successfully increased by substitution of residues within its reaction center and deletion from its C-terminus, respectively. Detailed analysis indicated that the increasing of activities was mainly due to the increasing of kcat values. The PH0925 protein, from the thermophilic euryarchaeon Pyrococcushorikoshii, has been identified as a bifunctional protein with phosphomannose isomerase and mannose-1-phosphate guanylyl transferase activities. The PH0925 mannose-1-phosphate guanylyl transferase activity was drastically increased by deletion of 114 residues from its C-terminus. These successful examples provide a helpful clue for artificial improvement of thermophilic enzymatic activities.
