π-π Interactions in structural stability: Role in superoxide dismutases.

In the present work, the influences of π-π interactions in superoxide dismutase (SOD) active centers were analyzed. The majority of the aromatic residues are involved in π-π interactions. Predominant type of interacting pairs is His-His and His-Trp pairs. In addition to π-π interactions, π residues also form π-networks in SOD proteins. The π-π interactions are most favorable at the pair distance range of 5-7 Å. We observed that most of the π-π interactions shows stabilization energies in the range from -4.2 to -12.6 kJ mol-1, while the metal assisted π-π interactions showed an energy in the range from -83.7 to -334.7 kJ mol-1. Most of the π-π interacting residues were evolutionary conserved and thus probably important in maintaining the structural stability of proteins through these interactions. A high percentage of these residues could be considered as stabilization centers, contributing to the net stability of SOD proteins. [ABSTRACT FROM AUTHOR]