Analysis of cation-π interactions using quantum chemistry and statistical analysis of high-resolution protein...

Cation-π interactions are widely considered key contributors to protein structure and molecular recognition, with quantum chemical studies often predicting substantial stabilization energies. However, their actual prevalence and strength in protein environments remain debated. Here, we combine high-level quantum chemical calculations with large-scale statistical analyses of high-resolution protein structures to reassess the role of lysine-π interactions. While gas-phase calculations confirm strong cation-π binding for idealized geometries, with corresponding energies of -19.0 kcal·mol^-1 and -16.0 kcal·mol^-1 for Lys-Phe and Arg-Phe pairs respectively, we demonstrate that even small geometric distortions and the inclusion of dielectric screening significantly reduce interaction energies to respective values of -5.9 kcal·mol^-1 and -6.5 kcal·mol^-1 at a dielectric constant of 6 and to -3.7 kcal·mol^-1 and -4.7 kcal·mol^-1 at a dielectric constant of 78. By leveraging the current size of the Protein Data Bank, we analyzed a much larger set of high-resolution protein structures than previously feasible, enabling a more rigorous evaluation of the structural prevalence of lysine-π interactions. Our statistical analysis reveals a low occurrence of geometries consistent with optimal cation-π interactions. By bridging quantum chemical results with structural data, this work reconciles the discrepancy between strong intrinsic interaction energies and their limited manifestation in proteins. These findings highlight the importance of geometric and environmental effects and suggest that Lys-π interactions in proteins are context-dependent and likely contribute less to protein structure than previously assumed.