Chemical modification and protein engineering, by searching for homologs in hyperthermophiles especially are useful tools for thermo stabilizing proteins, and also for elucidating the mechanism of protein stability that a single or a few amino acid replacement(s) in a protein is/are sufficient to enhance protein thermostability. Many eukaryotes have no homologs protein in the thermophilic organism; protein engineering would be necessary in such cases. Protein engineering may involve directed evolution. The factors affecting the thermal stability of proteins have been identified by comparison...