Data Sheet 2_The amino acid composition of mammalian mitochondrial proteins correlates with generation time.zip

Previous studies observed a correlation between the GC contents of the 12 mitochondrial protein-coding genes encoded on the H-strand and the generation times of mammals. However, how variation in GC content influences the amino acid composition of the proteins of these genes remains unclear. To examine this, we analyzed these mitochondrial proteins from 1,208 mammalian species. We first estimated the expected amino acid frequencies based on base frequencies at each codon position and then calculated the observed amino acid frequencies. The expected and observed proportions of almost half of the amino acids (8-9) showed a positive correlation with mammalian generation times, whereas the remaining amino acids (11-12) had a negative relationship. Accordingly, we categorized these amino acids as Group I and Group II, respectively. While the proportion of Group I amino acids showed a significant positive relationship with generation time, the magnitude of correlation was five times greater for highly variable amino acids than that observed for conserved amino acids. As expected, the opposite pattern was observed for the Group II amino acids. These findings are important because amino acid composition influences the structure and function of mitochondrial proteins. Our results suggest that for Group I amino acids, the magnitude of this influence is likely to be greater for mammals with long generation times (e.g., primates) than in those with short generation times (e.g., rodents).