title: Experimental evidence for the thermophilicity of ancestral life.
abstract: Theoretical studies have focused on the environmental temperature of the universal common ancestor of life with conflicting conclusions. Here we provide experimental support for the existence of a thermophilic universal common ancestor. We present the thermal stabilities and catalytic efficiencies of nucleoside diphosphate kinases (NDK), designed using the information contained in predictive phylogenetic trees, that seem to represent the last common ancestors of Archaea and of Bacteria. These enzymes display extreme thermal stabilities, suggesting thermophilic ancestries for Archaea and Bacteria. The results are robust to the uncertainties associated with the sequence predictions and to the tree topologies used to infer the ancestral sequences. Moreover, mutagenesis experiments suggest that the universal ancestor also possessed a very thermostable NDK. Because, as we show, the stability of an NDK is directly related to the environmental temperature of its host organism, our results indicate that the last common ancestor of extant life was a thermophile that flourished at a very high temperature.
authors.affiliation: Department of Applied Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Akanuma
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Yokobori
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Kimura
authors.forename: Naoki
authors.initials: N
authors.lastname: Nemoto
authors.forename: Tomoko
authors.initials: T
authors.lastname: Mase
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Miyazono
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yamagishi
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics; D016384:Consensus Sequence; D018360:Crystallography, X-Ray; D004795:Enzyme Stability / Q000235:genetics*; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009701:Nucleoside-Diphosphate Kinase / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D000069497:Origin of Life; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013696:Temperature
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D009701:Nucleoside-Diphosphate Kinase
keywords: ancient protein; crystal structure; last universal common ancestor; molecular resurrection; phylogenetic analysis