[Minimum directed dipole-dipole interactions-criteria for formation of globular proteins]

The influence of the dipole-dipole interactions in different secondary structure types is analysed. It is calculated that the values of peptide unit dipole moment projections on the helical axial vector and on the vector, perpendicular to the axis, differ markedly for the alpha-helical conformation (the dipole moment axial component is the maximum and equal to 3,34 debye) and for the extended conformations--beta- and poly-1-proline II type (axial component is the minimum and equal to 0.025 debye; perpendicular component is the maximum). In the course of study it has been suggested that the minimum size of the beta-structure stable fragment is two and of poly-1-proline II type helix--three residues. Taking into account that the dipole moment perpendicular components can be compensated along one complete helical turn, some general conclusions concerning protein folding can be made. The number of folding variants for the alpha-helical proteins is limited, whereas for the beta-structure type proteins they are numerous.