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.