Insight into the mechanism of protein thermostability based on the residue interaction degrees

ABSTRACT Understanding the basis of protein thermostability raises a general question: which residue with specific interaction degrees is more important to the protein thermostability? A strictly selected dataset of 131 pairs of thermophilic (TPs) and mesophilic proteins (MPs) was constructed. There were 6.4% and 8.4% of the total residues in sequences did not interact with others in TPs and MPs. The amino acid contents in sequences are closest to those with the interaction degrees of 3 according to the Chi-squared distances. Only Glu, Gln and the amide residues showed significant differences in sequences, which was the same as identified at low residue interaction degrees. However, we observed significant Phe, Lys, Leu, Gln and the charged, aliphatic, aromatic, positive charged and small residues at high interaction degree. Among them, Phe was rarely reported previously although aromatic residues were well-known contributor to protein thermostability. Finally, we took aspartate transcarbamylases as an example to explain how a residue with various interaction degrees contributed differently to their thermostability. Our results clearly demonstrated the differences of amino acids in sequence between TPs and MPs could only represent those involved in low interaction degrees. Much more residues with significant differences existed at high interaction degrees even if they had few significant amino acids in sequences. The interaction degree-based method should be an alternative tool in extracting valuable eigenvalues for predicting proteins attributes in bioinformatics. It could also provide a new perspective for studying the thermostability of proteins and engineering novel thermostable proteins. List of abbreviations TPs thermophilic proteins MPs mesophilic proteins OGT optimal growth temperature ASA absolute surface areas