科研之友
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摘要
S-aromatic motifs are important noncovalent forces for protein stability and function but remain poorly understood. Hence, we performed quantum calculations at the MP2(full)/6-311++G(d,p) level on complexes between Cys (H2S, MeSH) and Met (Me2S) models with models of Phe (benzene, toluene), Trp (indole, 3-methylindole), Tyr (phenol, 4-methylphenol), and His (imidazole, 4-methylimidazole). The most stable gas-phase conformers exhibit binding energies of -2 to -6 kcal/mol, and the S atom lies perpendicular to the ring plane. This reveals preferential interaction with the ring pi-system, except in the imidazoles where S binds edge-on to an N atom. Complexation tunes the gas-phase vertical ionization potentials of the ligands over as much as 1 eV, and strong sigma- or pi-type H-bonding supports charge transfer to the H-bond donor, rendering it more oxidizable. When the S atom acts as an H-bond acceptor (N/O-H-ar center dot center dot center dot S), calibration of the CHARMM36 force field (by optimizing pair-specific Lennard-Jones parameters) is required. Implementing the optimized parameters in molecular dynamics simulations in bulk water, we find stable S aromatic complexes with binding free energies of -0.6 to -1.1 kcal/mol at ligand separations up to 8 angstrom. The aqueous S-aromatics exhibit flexible binding conformations, but edge-on conformers are less stable in water. Reflecting this, only 0.3 to 10% of the S-indole, S-phenol, and S-imidazole structures are stabilized by N/O-H-ar center dot center dot center dot S or S-H center dot center dot center dot O-ar/N-ar sigma-type H-bonding. The wide range of energies and geometries found for S aromatic interactions and their tunable redox properties expose the versatility and variability of the S-aromatic motif in proteins and allow us to predict a number of their reported properties.
- 出版日期2018-4-12
