tailieunhanh - Báo cáo khoa học: A single amino acid substitution of Leu130Ile in snake DNases I contributes to the acquisition of thermal stability A clue to the molecular evolutionary mechanism from cold-blooded to warm-blooded vertebrates

We purified pancreatic deoxyribonucleases I (DNases I) from three snakes, Elaphe quadrivirgata, Elaphe climaco-phoraandAgkistrodon 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 mam-malian wild-type enzyme levels | Eur. J. Biochem. 270 307-314 2003 FEBS 2003 doi A single amino acid substitution of Leu130Ile in snake DNases I contributes to the acquisition of thermal stability A clue to the molecular evolutionary mechanism from cold-blooded to warm-blooded vertebrates Haruo Takeshita1 Toshihiro Yasuda2 Tamiko Nakajima1. Kouichi Moai1. Yasushi Kaneko1. Reiko Iida3 and Koichiro Kishi1 1Department of Legal Medicine Gunma University School of Medicine Maebashi Japan department of Biology and 3Department of Legal Medicine Fukui Medical University Matsuoka Japan We purified pancreatic deoxyribonucleases I DNases I from three snakes Elaphe quadrivirgata Elaphe climaco-phora 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 .