Research On The Relationship Between Main Chain Dihedral Angles And Side Chain Dihedral Angles Of Amino Acids Of Lysozyme Based On Mutual Information

As a kind of glycoside hydrolases,lysozyme widely exists in nature.It has antibacterial,antiinflammatory and antiviral effects by hydrolyzing bacteria cell wall effectively and dissolving the bacteria.It can also combine with viral protein directly and inactivate the virus.Lysozyme has three main types.The most studied type is C type of lysozyme.The C type of lysozyme is a single chain protein generally composed of 129 amino acids that contains 18 kinds of amino acids residues.Lysozyme is the first enzyme analyzed by X-ray.Subsequently,a lot of lysozyme structures have been solved at high resolution in different crystal forms: tetragonal,triclinic,monoclinic and orthorhombic forms.Because of its stability,solubility and ease of crystallization,lysozyme is one of the most studied protein in biological crystallography.The structure and function of lysozyme are relatively clear.In the PDB Bank,we can get a lot of crystal structures of lysozyme for research.This research handled many existing main chain dihedral angle data files and side chain dihedral angle data files of amino acids of lysozyme,and calculated the mutual information between main chain dihedral angles and side chain dihedral angles of amino acids in different files.We found that the mutual information of most of amino acid sites containing side chains were in the range of 0 to 0.2.However,the mutual information of 19 amino acid sites ranged widely.Then the analysis of the amino acids whose mutual information were greater than 0.3 showed the 13 amino acids whose mutual information were greater than 0.3 just right matched the amino acids whose mutual information ranged widely.The researches of 19 amino acids whose mutual information ranged widely on their properties,the relationships with the secondary structure of lysozyme,the interactions with the adjacent groups,and the relations with the catalytic domain of lysozyme indicated they were mainly polar amino acids and hydrophilic amino acids.They had relatively long side chains and activated functional groups.All of them were in chains,not rings.They were not located in α-helix and β-sheet structure,mainly in the Turn structure.There were relatively more adjacent activated functional groups around the amino acids whose mutual information were greater than 0.3.SER36 and GLN57 were near lysozyme’s catalytic sites GLU35 and ASP52.The rest amino acids seemed to distribute symmetrically near the prominent cleft between lysozyme’s two domains.Thereinto,the 13 amino acids whose mutual information were greater than 0.3 were inclined to distribute in the middle of lysozyme protein,and the remaining 6 amino acids were inclined to distribute at both ends of the lysozyme protein.This research has laid a solid foundation for a better understanding the relationship between main chain dihedral angles and side chain dihedral angles of amino acids and has made a further explanation for the meaning of mutual information to the relationship between main chain dihedral angles and side chain dihedral angles of amino acids.