Thermophiles include eubacteria, archaea and some fungi. These organisms are optimally grown in the range of 45–80☌ temperature, whereas this range of the mesophilic organisms is 15–45☌. And their hydrophilicity is negatively associated with the corresponding hydrophobicity (r = -0.493, p<0.001 and r = -0.324, p<0.05) suggesting their reciprocal evolvement.ĭiscovery of the bacterium Thermus aquaticus initiates a significant and active research on the thermostable organisms. Pearson’s correlation result suggests that the isoelectric points of mesophilic and thermophilic proteins are positively correlated (r = 0.93 and 0.84, respectively p<0.001) to their corresponding charges. The Ramachandran plot/ data suggest a higher abundance of the helix, left-handed helix, sheet, nonplanar peptide and lower occurrence of cis peptide, loop/ turn and outlier in thermophiles. The GLU-HIS and GLU-LYS salt-bridge dyads are calculated to be significantly higher (p<0.05 and p<0.001, respectively) in thermophilic and GLU-ARG is higher in the mesophilic proteins. The average percentage of salt-bridge of thermophiles is found to be higher by 20% than their mesophilic homologue.
The 60% thermophiles are found with higher number of salt bridges in this study. The possible sites for Tyr phosphorylation are noticed to be 25% higher (p<0.05) in thermophilic proteins. 0.6, p<0.01, respectively) in thermophilic proteins compared to their mesophilic counterpart. The mean differences of isoelectric points and charges are found to be significantly less (7.11 vs. A consistent lower distribution of thermophilicity and discretely higher distribution of hydrophobicity is noticed in a large number of thermophilic versus their mesophilic protein homolog. Phospho-regulated Tyr and redox-sensitive Cys are also moderately distributed ( χ 2~20.0, p<0.01) in a larger number of thermophilic proteins. These results provide a putative mechanism for the control of protein-folding initiation and growth by polar/nonpolar sequence propensity alone.Present results strongly suggest that nonpolar smaller volume amino acids Ala ( χ 2 = 238.54, p<0.001) and Gly ( χ 2 = 73.35, p<0.001) are highly and Val moderately ( χ 2 = 144.43, p<0.001) occurring in the 85% of thermophilic proteins.
#NONPOLAR HYDROPHOBIC AMINO ACIDS FREE#
A near-perfect correlation was observed between the areas of the molecule that are present in the burst-phase kinetic intermediate and both the free energy of formation of hydrophobic initiation sites and the parameter "average area buried upon folding," which pinpoints large side chains, even those containing charged or polar portions. Recent experiments on the folding of mutant apomyoglobins provides corroboration for models based on the hypothesis that folding initiation sites arise from hydrophobic interactions. Folding initiation sites might therefore contain not only accepted "hydrophobic" amino acids, but also larger charged side chains.
For example, a lysine side chain contains four methylenes, which may undergo hydrophobic interactions if the charged epsilon-NH(3)(+) group is salt-bridged or hydrogen-bonded. It has previously been noted that many amino acid side chains contain considerable nonpolar sections, even if they also contain polar or charged groups. A primary thermodynamic driving force for the formation of globular structure is thus the sequestration of nonpolar groups, but the correlation between the parts of proteins that are observed to fold first (termed folding initiation sites) and the "hydrophobicity" (as customarily defined) of the amino acids in these regions has been quite weak.
Globular proteins fold by minimizing the nonpolar surface that is exposed to water, while simultaneously providing hydrogen-bonding interactions for buried backbone groups, usually in the form of secondary structures such as alpha-helices, beta-sheets, and tight turns.