Analysis of cation–π interactions to the structural stability of RNA binding proteins

Cation–π interactions play an important role to the stability of protein structures. In this work, we have analyzed the influence of cation–π interactions in RNA binding proteins. We observed cation–π interactions in 32 out of 51 RNA binding proteins and there is a strong correlation between the number of amino acid residues and number of cation–π interactions. The analysis on the influence of short (<±3 residues), medium (±3 or ±4 residues) and long range contacts (>±4 residues) showed that the cation–π interactions are mainly formed by long-range contacts. The cation–π interaction energy for Arg–Trp is found to be the strongest among all interacting pairs. Analysis on the preferred secondary structural conformation of the residues involved in cation–π interaction indicates that the cationic Lys and Arg prefer to be in α-helices and β-strands, respectively, whereas the aromatic residues prefer to be in strand and coil regions. Most of the cation–π interactions forming residues in RNA binding proteins are conserved among homologous sequences. Further, the cation–π interactions have distinct roles to the stability of RNA binding proteins in addition to other conventional non-covalent interactions. The results observed in the present study will be useful in understanding the contribution of cation–π interactions to the stability of RNA binding proteins.