Comment on elastic network models and proteins.

Elastic network models have been used to study the properties of coarse grained models of proteins and larger biomolecular complexes. In this comment, we point out that it is important to build rotational symmetry, as well as translational symmetry, into these models that are designed to describe the rigidity, and the associated low-frequency deformations. This leads to strong restrictions on what form of interactions can be used. In particular, the only allowed two-center harmonic interactions are those corresponding to Hooke springs. Additional complexity can be introduced if required by using three-center harmonic interactions.