An electronic orbital of a dihedral angle of a molecular chain is introduced. A tight-binding Hamiltonian on the basis of the dihedral orbitals is defined. This yields the Green's function between two dihedral angles of the chain. It is revealed that the Green's function, which we refer to as the electronic communicability, is useful in differentiating protein molecules of different types of conformation and secondary structure. (c) 2007 Elsevier B.V. All rights reserved.