Contribution of anion-pi interactions to the stability of Sm/LSm proteins

We have analyzed the influence of anion-pi interactions to the stability of Sm/LSm assemblies. The side chain of Glu is more likely to be in anion-pi interactions than Asp. Phe has the highest occurrence in these interactions than the other two pi residues. Among the anion-pi residue pairs, Glu-Phe residue pair showed the maximum number of anion-pi. We have found hot-spot residues forming anion-pi interactions, and Glu-Phe is the most common hot-spot interacting pair. The significant numbers of anion-pi interacting residues identified in the dataset were involved in the formation of multiple anion-pi interactions. More than half of the residues involved in these interactions are evolutionarily conserved. The anion-pi interaction energies are distance and orientation dependent. It was found that anion-pi interactions showed energy less than -15 kcal mol(-1), and most of them have energy in the range -2 to -9 kcal mol(-1). Solvent accessibility pattern of Sm/LSm proteins reveals that all of the interacting residues are preferred to be in buried regions. Most of the interacting residues preferred to be in strand. A significant percentage of anion-pi interacting residues are located as stabilization centers and thus might provide additional stability to these proteins. The simultaneous interaction of anions and cations on different faces of the same pi-system has been observed. On the whole, the results presented in this work will be very useful for understanding the contribution of anion-pi interaction to the stability of Sm/LSm proteins