Figure 3. The average amino acid composition of the Hsp60 sequences from 19 phyla: a - Heat map displaying normalized average PID values between 19 phyla of Hsp60 sequences; b - The average amino acid composition of the Hsp60 sequences for each of the 19 phyla compared to the corresponding proteomic values. In Figure 3a the average values were normalized using the min-max normalization method. The line “Summary” presents the average normalized amino acid composition of Hsp60 for 19 phyla. In Figure 3b the amino acid profiles were represented as the average amino acid composition of Hsp60 for each of 19 phyla compared to the average amino acid composition of the respective proteomes. The structure of color scale is as follows: Higher/Lower - the amino acid content in Hsp60 is higher/lower than in proteomes, respectively; Comparable - the amino acid content in Hsp60 is comparable to the average proteomic value. The “Summary” line shows the average amino acid profile of Hsp60 for 19 phyla. The groups were sorted using the NCBI Taxonomy. Amino acids were sorted using an average amino acid composition of 19220 Hsp60 sequences.
As can be seen, aliphatic (Ala, Val, Gly, Leu, and Ile), charged (Glu, Lys, Asp), and polar (Thr) amino acid residues are overrepresented in the Hsp60 sequences of all 19 phyla (Figure 3a). The average content of these amino acid residues for 19220 Hsp60 sequences ranges from 6.2±1.1% for Thr to 12.7±1.9 for Ala (Supplementary, AA composition of Hsp60). In turn, aromatic amino acid residues (Phe, Tyr, His, and Trp) and Cys are underrepresented and their content ranges from 0.2±0.3% (Cys) to 1.6±0.4% (Phe) (Figure 3a; Supplementary, AA composition of Hsp60).
To assess the amino acid composition of Hsp60s relative to proteomic values (Supplementary, AA Composition of proteomes), amino acid profiles of Hsp60 sequences were determined for each of 19 phyla (Figure 3b).
The average content of aliphatic (Ala, Val, Gly, and Ile), charged (Glu, Lys, and Asp), and polar (Thr) amino acid residues in Hsp60 sequences is not only high, but also higher than the average proteomic values for almost all phyla (Figure 3b). The high content of aliphatic amino acid residues may indicate the structural stability of these proteins15. The content of Pro, aromatic (Phe, Tyr, His, and Trp) and polar (Ser and Cys) amino acid residues was low and lower compared to the average proteomic values. In general, according to the summary amino acid profile, no matter how evolutionarily distant the 19 phyla are from each other, the amino acid composition of their Hsp60 sequences remained the same, as its correlation with the amino acid composition of the corresponding proteome.
Despite the low PID values both within and between phyla, functionality and domain structure41–45 of Hsp60 persisted over time. It can be assumed that these features largely depended on the amino acid composition, i.e. on the percentage content of amino acids in Hsp60.