The interaction between phenylalanine rings in proteins

AbstractAn analysis has been made of the geometry of phenylalanine-phenylalanine interactions in proteins of known structure. 162 Phe-Phe interactions were found with C-C distances less than 4.6 Å. Three angles were used to define the geometry of interaction, P = the angle betwen ring planes, and polar coordinates, Tθ, Tϕ to specify the relative spatial disposition of the two rings. The overall distribution of P values is the same as that expected for a random distribution of planes in 3 dimensions; i.e. the majority, of interactions have P approaching 90°. However, for high Tθ values (when one Phe lies directly above the ring of the other Phe) the distribution is non-random, and a preference for perpendicular interactions is expressed. This preference is in accord with recent quantum-mechanical calculations