A single amino acid substitution of Leu130Ile in snake DNases I contributes to the acquisition of thermal stability.
We purified pancreatic deoxyribonucleases I (DNases I) from three snakes, Elaphe quadrivirgata, Elaphe climacophora and Agkistrodon blomhoffii, and cloned their cDNAs. Each mature snake DNase I protein comprised 262 amino acids. Wild-type snake DNases I with Leu130 were more thermally unstable than wild-type mammalian and avian DNases I with Ile130. After substitution of Leu130Ile, the thermal stabilities of the snake enzymes were higher than those of their wild-type counterparts and similar to mammalian wild-type enzyme levels. Conversely, substituting Ile130Leu of mammalian DNases I made them more thermally unstable than their wild-type counterparts. Therefore, a single amino acid substitution, Leu130Ile, might be involved in an evolutionally critical change in the thermal stabilities of vertebrate DNases I. Amphibian DNases I have a Ser205 insertion in a Ca2+-binding site of mammalian and avian enzymes that reduces their thermal stabilities [Takeshita, H., Yasuda, T., Iida, R., Nakajima, T., Mori, S., Mogi, K., Kaneko, Y. & Kishi, K. (2001) Biochem. J.357, 473-480]. Thus, it is plausible that the thermally stable wild-type DNases I of the higher vertebrates, such as mammals and birds, have been generated by a single Leu130Ile substitution of reptilian enzymes through molecular evolution following Ser205 deletion from amphibian enzymes. This mechanism may reflect one of the evolutionary changes from cold-blooded to warm-blooded vertebrates.
Takeshita
Haruo
H
Department of Legal Medicine, Gunma University School of Medicine, Maebashi, Japan.
Yasuda
Toshihiro
T
Nakajima
Tamiko
T
Mogi
Kouichi
K
Kaneko
Yasushi
Y
Iida
Reiko
R
Kishi
Koichiro
K
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D005075:Biological Evolution; D001833:Body Temperature Regulation / Q000235:genetics; D019556:COS Cells; D003850:Deoxyribonuclease I / Q000235:genetics*; D004795:Enzyme Stability / Q000235:genetics*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010179:Pancreas / Q000378:metabolism; D010802:Phylogeny; D012911:Snakes / Q000235:genetics*; D013696:Temperature
D003850:Deoxyribonuclease I