Distribution of dipole moments in tertiary structures of globular proteins

It's well known that conformational transitions in protein systems are usually observed as a reply to joining of substrates, effectors, ions, or as result of protein-protein and protein-DNA interactions. In many cases it is expressed in mutual rotations of separate segments, domains, whole subunits or multiglobular proteins. In all such cases distributions of charges and dipole moments in globular proteins play an important role, while the last play a key role in phenomena of segment mobility.

This work proposes analysis of dipole moment distributions in the spatial structures of proteins. Values of dipole moments were calculated by definition of dipole moments of atom groups as sum of products of known standard charge and distance of each atom. This values were obtained for each amino acid separately whose total charge was assumed to be compensated as well as for each peptide group and side radical. The proteins were selected from the last version of PDB with high resolution and without breaks in chain. As this bank has a lot of complexes of molecules each molecule in such complex was considered to be a separate molecule.

As result of this work we can say that in large proteins dipole moment of peptide groups play the basic role. Normalized difference of values of total dipole moment and dipole moment of peptide groups goes to zero in increasing of protein size. Normalized values of total dipole moments have a periodicity in the range of 100 - 200 amino acids. It is shown that maximal value of total dipole moment is reached 400 D with 45% of -helix amino acid residues, while the maximal value of total dipole moment is reached for proteins with 20% of -sheet amino acid residues. Further increasing of ration of -sheet amino acid residues fall the value of total dipole moment of proteins, so we can say that -sheet residues strictly minimize dipole moment of a protein.