title: Stacking and T-shape competition in aromatic-aromatic amino acid interactions.
abstract: The potential of mean force of interacting aromatic amino acids is calculated using molecular dynamics simulations. The free energy surface is determined in order to study stacking and T-shape competition for phenylalanine-phenylalanine (Phe-Phe), phenylalanine-tyrosine (Phe-Tyr), and tyrosine-tyrosine (Tyr-Tyr) complexes in vacuo, water, carbon tetrachloride, and methanol. Stacked structures are favored in all solvents with the exception of the Tyr-Tyr complex in carbon tetrachloride, where T-shaped structures are also important. The effect of anchoring the two alpha-carbons (C(alpha)) at selected distances is investigated. We find that short and large C(alpha)-C(alpha) distances favor stacked and T-shaped structures, respectively. We analyze a set of 2396 protein structures resolved experimentally. Comparison of theoretical free energies for the complexes to the experimental analogue shows that Tyr-Tyr interaction occurs mainly at the protein surface, while Phe-Tyr and Phe-Phe interactions are more frequent in the hydrophobic protein core. This is confirmed by the Voronoi polyhedron analysis on the database protein structures. As found from the free energy calculation, analysis of the protein database has shown that proximal and distal interacting aromatic residues are predominantly stacked and T-shaped, respectively.
authors.affiliation: Dipartimento di Chimica, Università di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Chelli
authors.forename: Francesco Luigi
authors.initials: FL
authors.lastname: Gervasio
authors.forename: Piero
authors.initials: P
authors.lastname: Procacci
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Schettino
mesh_terms: D003198:Computer Simulation; D004151:Dipeptides / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D010649:Phenylalanine / Q000737:chemistry*; D011487:Protein Conformation; D013499:Surface Properties; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D004151:Dipeptides; D014443:Tyrosine; D010649:Phenylalanine