Analysis of amino acid substitution rate in proteins between hypert hermophilic and mesophilic organisms using complete genome data

摘要

Hyperthermophilic organisms (both bacteria and archaea) grow optimally at temperatures above 80 deg C. Proteins from these organisms are heatstable under extreme conditions, where their homologous from mesophilic organisms denature. Because recent progress of genome projects revealed complete nucleotide sequence of many microbial genomes, we have compared their amino acid sequences and compositions in proteins between hyperthermophilic (9 species) and mesophilic organisms (26 species). At first, wehave chose a hyperthermophilic archaeon Pyrococcus furiosus that grow around at 100 deg C as a model organism. Because the complete nucleotide sequence of the organism is available from Utah genome Center and we used to work with the organism in our experimental biological laboratory. Homologous genes of P. furiosus were extracted from 9 hyperthermophile and 26 mesoplile complete genomes by using FASTA program. We have developed computer programs and counted single substitution polymorphism of nucleotide and amino acid sequences of these homologous genes. In order to compare the differences of substitution tendency, we calculated ratios between mesophile and thermophile substitution polymorphism (denominator is thermophile), and the substitution matrix of nucleotide and amino acid were made based on logarithmic odds ratio from the results of single substitution polymorphism.