Nature of cation-π interactions and their role in structural stability of immunoglobulin proteins

Cation-π interactions are known to be important contributors to protein stability and ligand-protein interactions. In this study, we have analyzed the influence of cation-π interactions in single chain immunoglobulin proteins. We observed 87 cation-π interactions in a data set of 33 proteins. These interactions are mainly formed by long-range contacts, and there is preference of Arg over Lys in these interactions. Arg-Tyr interactions are predominant among the various pairs analyzed. Despite the scarcity of interactions involving Trp, the average energy for Trp-cation interactions is quite high. This information suggests that the cation-π interactions involving Trp might be of high relevance to the proteins. Secondary structure analysis reveals that cation-π interactions are formed preferably between residues in which at least one is in β-strand. Proteins having β-strand regions have the highest number of cation-π interaction-forming residues.